Explosion! The Museum of Naval Firepower, Gosport, UK

Established in 2001 in the former Royal Naval Armaments Depot at Priddy's Hard on the Gosport side of Portsmouth Harbour, Explosion! The Museum of Naval Firepower has been part of the multi-location National Museum of the Royal Navy since 2013.  With a focus on naval armaments from the 18th century to the present, the museum contains a range of weaponry, from cannons and gun turrets to torpedoes and missiles.  

For over 200 years, Priddy's Hard was the site of a fort and then a weapons and ammunition depot for the Royal Navy and the British Army.  By a legislative act of 1750, a 40-acre parcel of agricultural land in Gosport was purchased by the Board of Ordnance for the purpose of extending the rampart defences of Portsmouth Harbour and the Royal Dockyard.  The site was named after the land's original owner, Jane Priddy, being manned by the Army and known as Priddy's Hard Fort.  Although gunpowder for Royal Navy warships had been stored in the Old Portsmouth district of the city of Portsmouth since the 1580s, a growing chorus of public complaints about the risk posed by this volatile powder led the Board of Ordnance to take the decision in 1769 to re-locate the powder to Priddy's Hard.  After six years of work, the new magazine (known as the Grand Magazine) opened in 1777, receiving its first delivery of gunpowder barrels in May of that year.  A high brick wall enclosed the magazine building to prevent the importation of contraband items, such as spark-generating metallic objects, alcohol, and smoking paraphernalia.  The 14 eighteen-pounder guns and fortifications of Priddy's Hard depot were manned from 1803 by artillery troops housed at nearby Forton Barracks and, from 1833, the depot itself was guarded by members of the Dockyard Police Force.  

Throughout the 19th and much of the 20th centuries, Priddy's Hard was used to store ammunition and weaponry used by the Royal Navy aboard its ships, by the local fortifications of Portsmouth Harbour, and by British forces deployed around the world.  Despite a storage capacity of 6,200 barrels (250 tons) of gunpowder in the Grand Magazine, the surging demand for powder during the Napoleonic Wars led to the use of floating powder hulks in the harbour and the construction of satellite depots at various locations in and around Portsmouth Harbour.  A number of additional magazines were also constructed at Priddy's Hard from the mid-19th century onwards, being named 'B', 'C', 'D', and 'E' magazines.  In 1847-48, the construction of the Portsmouth Laboratory on the Priddy's Hard site marked a shift from munitions storage to munitions manufacturing and, by the 1860s, the principal work of the Portsmouth Laboratory was the filling of land and naval artillery shells and the preparation of fuzes for those shells.  

As new explosives (nitro-glycerine, gun cotton, ballastine, cordite, lyddite) were developed, changes were made to Priddy's Hard to accommodate the requirements of these substances and the need to separate the most dangerous testing and filling operations from the storage areas.  To transport powder and ammunition between various buildings on the Priddy's Hard site, a narrow-gauge 'shell tramway' was constructed in the 1860s, with manual propulsion being replaced in 1929 by battery-driven locomotives.  The acquisition of electric road tractors and trailers led to the decommissioning of the shell tramway in 1960 and the paving over of the tramway tracks.  Priddy's Hard underwent constant change in the 20th century, with a surge of activity during the First and Second World Wars requiring the construction of new buildings on the site.  Focused on filling shells and cartridges rather than storage of munitions, Priddy's Hard became the principal local depot, responsible for supplying ammunition as well as servicing and repairing all types of naval weaponry.  During the Second World War, 2,500 women replaced male employees who enlisted in the military.  

As activity at Priddy's Hard waned after the Second World War, the original 18th century buildings on the site were converted into an in-house museum of naval ordnance in 1971.  By 1977, a Ministry of Defence memorandum laid out a plan to wind up operations at Priddy's Hard and transfer activities to other nearby facilities over the next decade.  Although the Falklands War of 1982 saw a short-term surge of activity at Priddy's Hard, this proved the last significant naval use of the facility.  The depot's rail link was decommissioned in 1986 and in 1988 the last stores and staff members were moved out.  After a thorough search of the entire site for any remaining explosives, Priddy's Hard was officially closed in September 1989.

                 

Photos taken 14 October 2019

Visitors to Portsmouth Historic Dockyard board the waterbus Jenny R for the short cross-harbour voyage to Explosion! The Museum of Naval Firepower in Gosport.  The vessel, with a maximum speed of 18 knots (33.3 km/h) and capacity for up to 75 passengers, is owned and operated by Solent & Wightline Cruises under contract to Portsmouth Historic Dockyard.

The Jenny R outward bound for Explosion! The Museum of Naval Firepower, located 1.5 kilometres away in Gosport, on the opposite side of Portsmouth Harbour.  Like the Royal Navy Submarine Museum, Explosion! is operated as part of the Portsmouth Historic Dockyard, with use of the waterbus included in the Portsmouth Historic Dockyard's 'Full Navy' ticket that provides full access to all attractions.

Looking over the stern of the Jenny R as Portsmouth recedes in the distance.  The distinctive Spinnaker Tower and the masts of the Victorian-era armoured frigate HMS Warrior (1860) can be seen.

One of the original brick buildings of the Royal Naval Armaments Depot Priddy's Hard.

The Depot Offices and Storehouse, built in 1812-13 and extended in 1920 to house stores, the cooperage, and a watch office.  Activity at Priddy's Hard increased steadily through the first decades of the 20th century due to the World Wars and the decision to close His Majesty's Gunwharf in Portsmouth in 1923, after which Priddy's Hard became the senior local depot for supplying ammunition and servicing all types of naval ordnance.  

The Grand Magazine, also known as 'A' Magazine, the first structure built at Priddy's Hard following the 1766 decision by the Ordnance Board to establish a new naval gunpowder storage depot in Gosport.  Construction of the Grand Magazine commenced in 1771 and was completed in 1777, with the facility capable of holding 6,200 barrels (250 tons) of gunpowder.  The Grand Magazine's 2.5 metre (8 foot) thick walls and its solid roof were designed to withstand a potential French bombardment.  Air gaps and vents in the magazine were designed to maintain a constant temperature inside.

The grounds of Explosion! The Museum of Naval Firepower display a number of large naval weapons systems, from mortars and deck guns to torpedo tubes and missile launchers.

A 13-inch mortar, dating to around 1810.  These weapons, weighing 4,500 kilograms (4.5 tons), were designed to counter enemy sieges of fortresses but could only fire at a fixed 45-degree angle.  They could lob an 88 kilogram (195 pound) mortar bomb to a range of 2.5 kilometres (1.66 miles), with the bomb coming down almost vertically onto enemy besieging troops.  Such 13-inch mortars were part of the defences at the forts on Portsdown Hill, protecting Portsmouth Dockyard against enemy attack.  As mortars were heavy, awkward, and difficult to use, they were phased of out service in the 1880s.  

A four-inch Quick Firing (QF) Mk XVI naval gun, the standard British naval gun of the Second World War.  In service between 1936 and the 1950s, the QF Mk XVI was the main armament of many smaller warships, such as destroyers, and also served as the secondary gun armament on larger ships like cruisers and battleships.  Although effective against surface targets, the Mk XVI was particularly useful against air targets, given a high rate of fire of 15-20 rounds per minute.  Aboard ships, the gun would have been protected by a gun shield, though the example exhibited here is lacking a shield and has had minor modifications made to it, likely for use ashore in a coastal defence role.  When fired at a 45-degree angle, the QF Mk XVI gun's range was 18 kilometres (11.2 miles), though this dropped to 11 kilometres (7 miles) when fired at an 80-degree angle in anti-aircraft mode.  The length of the gun is 4.83 metres (190 inches) and it weighs 2,042 kilograms (2 tons).  Manned by a crew of at least five men, the QF Mk XVI fired high explosive shells weighing 16 kilograms (35 pounds) or armour piercing shells weighing 17 kilogram (38 pounds).      

A 4.7-inch Mk IXB gun on a central pivot Mk XXII single mounting, dating from 1942.  The 4.7-inch gun, weighing 3,024 kilograms (2.9 tons), was the main armament of Royal Navy destroyers during the Second World War and was used against surface, air, and land targets.  The Mk IXB gun on a Mk XXII mounting was used on the S-, T-, U-, V-, and W-class destroyers of the Royal Navy, many of which served as fleet and convoy escorts during the war.  With a notional rate of fire of 12 rounds per minute, this was greatly reduced in bad weather such as that experienced on the Arctic convoy routes to Russia.  The Mk IXB gun, manufactured by Vickers-Armstrong, was served by a seven-man crew and fired shells weighing 22 kilograms (50 pounds) to a range of 15.5 kilometres (9 miles) at an elevation of 40 degrees.  The 4.7-inch gun served aboard Royal Navy ships until the 1970s.     

A Quick Firing (QF) 4.5-inch Mk 5 gun on a twin Mk 6 mounting.  The 4.5-inch gun entered service in 1947 as a replacement for the 4.7-inch gun and equipped Royal Navy destroyers and frigates built in the 1950s and 1960s.  Designed as a dual purpose weapon against surface targets and aircraft, the Mk 5 gun was the last of the Royal Navy's major gun systems requiring a crew.  The Mk 5's six-man crew could fire fourteen 24.9 kilogram (55 pound) shells per minute to a range of 19 kilometres (11.7 miles).  In anti-aircraft service, the Mk 5 gun could fire to an altitude 12,500 metres (41,000 feet).  The Mk 5 gun is 6.13 metres (20 feet) in length and weighs 2,859 kilograms (2.8 tons).  

A Shipborne Torpedo Weapon System (STWS2), also known as the Mk 32 surface vessel torpedo tubes.  Although designed to fire either the Mk 46 torpedo or the Sting Ray torpedo, the STWS2 was optimised for the Sting Ray, an advanced lightweight acoustic homing torpedo that automatically seeks out and attacks enemy submarines.  The STWS2 was fitted aboard Royal Navy warships beginning in the 1980s and requires only three men to load each of the three tubes.  The system is linked directly to the ship's  weapons computer for targeting and launch and controlled by the sonar operator in the ship's weapon control centre.  The Sting Ray torpedo, which entered service in 1983, has a range of eight kilometres (five miles) and is propelled by an electrically-powered pump jet engine that permits high speed, deep diving ability, agility, and low noise levels.

The 4.5-inch Mk 8 Mod 0 gun from the Type 42 destroyer HMS Liverpool (D92).  After being fired upon by a Libyan artillery battery in May 2011 while operating off the Libyan coast, HMS Liverpool used this gun to return fire, destroying the enemy battery immediately.  HMS Liverpool was  decommissioned on 30 March 2012 and this gun was subsequently donated to the museum.  Entering service in 1973 as a replacement for the QF 4.5-inch Mk 5 dual mount gun, the Mk 8 gun has equipped Royal Navy destroyers and frigates commissioned from the 1980s onwards.  Manufactured by Vickers, the Mk 8 gun weighs 2,438 kilograms (2.4 tons) and measures 6.22 metres (20 feet) in length.  As the Royal Navy's first medium-calibre gun requiring no crew in the mounting itself, the gun is operated by six crewmen remotely.  In semi-automatic mode, the gun can fire 25 rounds per minute, each weighing 36.5 kilograms (80.5 pounds).  Ammunition is fed up to the gun from the ship's magazine located three decks below and is loaded into the breech by automated handling gear.      

The Dutch-developed Goalkeeper Close-in Weapon System (CIWS), an autonomous and completely automatic weapon system with its own radar and sensors, designed for short-range defence of ships against missiles, aircraft, and high-speed surface vessels.  Intended as a ship's last-line of defence, Goalkeeper's onboard computer automatically detects, evaluates, and responds to any hostile threats approaching the ship, firing a barrage of 4,200 rounds of 30mm ammunition per minute from seven revolving barrels to literally shred incoming targets.  The Goalkeeper mounting weighs 6,372 kilograms (6 tons) and has a range of 350-2,000 metres (1,150-6,500 feet) depending on the ammunition used.  The Royal Navy employed Goalkeeper on Invincible-class aircraft carriers, Albion-class amphibious warfare ships, and Type 22 Batch 3 frigates between 1980 and 2015.  The Goalkeeper mounting displayed on the museum grounds was originally fitted aboard the aircraft carrier HMS Illustrious before being transferred to the navy's maritime warfare school (HMS Collingwood) in Fareham, UK for training purposes. 

A Sea Wolf Guided Weapon System (GWS-25) missile launcher.  A short-range guided missile, Sea Wolf is designed to protect warships against incoming missile and air attacks and is capable of tracking and destroying sea-skimming targets the size of a cricket ball travelling at supersonic speed.  Manufactured by British Aerospace (now MBDA UK Ltd), the 82 kilogram (180 pound) Sea Wolf missile entered service in 1979 and measures 1.9 metres (6 feet) long, with a diameter of 300 millimetres (12 inches) and a 14 kilogram (30.9 pound) high-explosive blast fragmentation warhead.  Travelling at Mach 3 (3,675 km/h), the Sea Wolf missile has a range of 6 kilometres (3.7 miles) and a maximum altitude of 3,000 metres (9,842 feet).  During the Falklands War of 1982, Royal Navy vessels equipped with Sea Wolf missiles attacked several hostile Argentine aircraft, often working in combination with other vessels fitted with the longer-range Sea Dart missile to form 'missile traps'.  Nevertheless, the failure of Sea Wolf to engage other Argentine aircraft led to the sinking of the Type 42 destroyer HMS Coventry and heavy damage to the Type 22 frigate HMS Glasgow.  Subsequent development work led to the creation of a longer-range, vertical launch variant (GWS-26) of Sea Wolf in the 1980s which equipped Royal Navy warships until the new Sea Ceptor missile began replacing Sea Wolf in 2017.           

A Sea Dart (GWS-30) missile launcher.  Manufactured by Hawker Siddeley Dynamics Ltd and later by British Aerospace, the Sea Dart missile entered Royal Navy service in 1973 as an area air defence weapon to protect the fleet from air attack.  It was fitted aboard Invincible-class aircraft carriers, Type 42 destroyers and to the sole Type 82 destroyer, HMS Bristol.  Launched by a solid-fuelled rocket booster and powered by a ramjet engine, the Sea Dart missile travelled at a speed of Mach 2.5 (3,087 km/h), homing in on its target using its onboard semi-active radar.  With an original range of 74 kilometres (46 miles), upgrades completed to the Sea Dart missile in 1989-1991 increased that range to 160 kilometres (92 miles).  The missile had a maximum altitude of over 11,000 metres (6 miles) and carried a warhead containing 11 kilograms (24 pounds) of high explosive.  Sea Dart missiles were used during the Falklands War of 1982, where they successfully destroyed several Argentine aircraft.  In February 1991, during the first Gulf War, a Sea Dart fired from the Type 42 destroyer HMS Gloucester became the first anti-air missile to down an enemy anti-ship missile at sea, successfully intercepting an Iraqi 'Seersucker' missile fired against the United States battleship USS Missouri.  Retired in 2012 after more than 40 years of service in the Royal Navy, the Sea Dart has been replaced by the Sea Viper anti-air missile system fitted aboard Type 45 destroyers.        

A display on the staff, with a focus on the wartime female staff, of the Royal Naval Armaments Depot Priddy's Hard greets visitors upon entering Explosion! The Museum of Naval Firepower.

One of several displays of various munitions greeting visitors as they beign their tour of the museum.  Suspended from the ceiling is an M349 metal transport cage designed for an anti-submarine mortar.  The large black bomb is an inert training variant of the Mk II Red Beard free-fall nuclear bomb, specifically designed to meet a joint Naval and Air Staff requirement for use in tactical situations and small enough to be carried by the Scimitar, Sea Vixen, and Buccaneer aircraft of the Fleet Air Arm.  Entering service in 1962, the Red Beard had an explosive power equivalent to 25 kilotons of high explosive, or almost twice that of the atomic bomb dropped on Hiroshima in 1945.  Red Beard bombs were carried aboard Royal Navy aircraft carriers deployed in the Far East and in the Atlantic.  Suffering from severe operational limitations and restrictions on arrested deck landings by aircraft carrying them, the Red Beard bomb was replaced by the end of the 1960s by the WE.177 free-fall nuclear bomb.     

One of a pair of bronze 'lionhead' swivel cannons manufactured in 1743 at the Royal Brass Foundry, Woolwich.  Mounted for part of their service lives on the Royal Yacht Victoria and Albert, these bronze cannons would use quarter-pound gunpowder charges to repel boarding parties at close quarters.  

A recreation of a Second World War-era Anderson shelter, named after Sir John Anderson, Lord Privy Seal in the British Government at the time and the man responsible for preparing the UK to withstand German air attacks.  The Anderson shelter was designed in 1938 and over 3.5 million were constructed during the Second World War.  Homeowners who earned over £250 per year paid £7 for a shelter, while those earning less were given a free shelter.  Made from corrugated metal sheets and steel plates, the shelters were half-buried into the ground and piled with earth on top to protect from bomb blasts.  Dark and damp inside, many families were reluctant to spend any time in their Anderson shelters, while others grew flowers and vegetables in the earth heaped on top.  After the war, the British government collected most shelters, though homeowners did have the option of purchasing their shelters for £1, with many homeowners converting them into garden sheds.

A display of 'magazine shoes', special footwear worn by workers at Priddy's Hard employed in explosive areas.  Made from leather and either sewn together or joined using wooden pegs or brass tacks, the shoes were designed to eliminate any risk of kicking sparks that could detonate the huge quantities of gunpowder stored at the facility.  The soles of magazine shoes required constant repair and were only worn in work areas and in the 'clean' walkways that connected rooms where explosives work was conducted.  All other areas of the facility were considered 'dirty'. 

Special work clothes hang in the Shifting Room, where those involved in working with or handling explosives would change from their street clothing into the special magazine clothing provided.  Workers would strip down to their underwear and have five minutes to change before stepping over a red line painted on the threshold indicating the transition from the 'dirty' to the 'clean' area of the facility.  Female workers wore baggy cream-coloured trousers, a collared slip, and a blue turban, with personal items worn in a cloth bag on a string around their necks.  

Life sized sculptures of munitions workers pushing trolleys of gunpowder barrels mark the route of the former 'Rolling Way' used to transfer gunpowder from Priddy's Hard's shoreside camber basin to the facility's magazine.  Gunpowder produced at the Royal Powder Manufactories at Faversham and Waltham Abbey was shipped on small sailing vessels down the Thames and along the south coast to Portsmouth, being unloaded in the the camber basin at Priddy's Hard and then carted to the magazine for storage.  Shells, mines, and other munitions containing the powder were packed at Priddy's Hard.  Finished munitions were similarly moved along the Rolling Way from the magazine to the basin to be loaded onto lighters for transport to warships moored offshore in the harbour.   

The Priddy's Hard Story, an exhibit on the history of the site and the development of the Royal Naval Armaments Depot Priddy's Hard between the late 18th century and its closure in 1989.  Exhibits to the left and right address the role of Priddy's Hard in the 'Age of Fighting Sail' and the late 19th and 20th centuries, respectively.   

Photos and maps tell the story of the development and activity of Priddy's Hard from the 1760s to the 1980s.

The entrance to a gallery devoted to the development of gunpowder during the Age of Fighting Sail, when Priddy's Hard stored and supplied powder to the wooden sailing ships of the 18th and 19th century Royal Navy.  Powder barrels were first stored at Priddy's Hard in 1777.  Gunpowder is comprised of approximately 15 parts charcoal to burn fiercely, 75 parts saltpetre to provide oxygen, and 10 parts sulphur which ignites easily and gives out immense heat.  While early 'serpentine gunpowder was formed by grinding these ingredients and hand mixing them into a dusty compound, later gunpowder was wet mixed and then dried to form a cake.  By the late 1700s, most gunpowder was 'corned', wherein the powder cake was broken up and forced through a sieve to form granules.  These granules were graded by size for different uses, hardened, and dried.  Corned powder burned more efficiently and evenly, and was less prone to separate out or give off toxic and highly-explosive dust.   

A Blomefield smooth bore muzzle loading gun, one of the most successful weapons of the Royal Navy, named after its developer, Thomas Blomefield.  The lack of decoration on the gun, especially around the muzzle, meant it was less likely to be damaged when fired.  Weighted towards its rear, the Blomefield gun was also very stable.  Blomefield guns served the Royal Navy from around 1750 to 1870, seeing action from the Battle of Trafalgar in 1805 to the Crimean War of 1853-56.

A display on the cooperage at Priddy's Hard.  It was in the cooperage that gunpowder barrels were made and repaired.  Priddy's Hard employed its first cooper, Isaac Whiston, from the time the facility opened in 1777.  The cooper earned three shillings a day, a good wage in that era.  The cooperage was in a line of offices and workshops that would later become the Main Office.  Materials and dimensions for gunpowder barrels were carefully prescribed by the Board of Ordnance, which was responsible for supplying ordnance to the armed forces.  A gunpowder barrel was made from wooden staves girded by four rivetted bands of copper and with 12 ashwood hoops secured with cooper nails or wooden pegs to even out the bulge of the barrel so as to make it easier to stack; no iron was used for hoops or nails out of fear of sparking the gunpowder with which the barrels would be filled.  

A brass cannon and bas-relief of a gun's crew and the munitions workers who made their work possible.  With the development of more advanced ordnance throughout the late 19th century, new forms of gunpowder were required.  Longer gun barrels required slower-burning powder to avoid bursting the barrels when firing shot and shells.  This led to the development of graphite-glazed hard powder and to powder pressed into different moulded shapes.  Eventually, British ordnance manufacturers classified 18 types of gunpowder, each designed for a particular class of weapon.  With the development of much more powerful cordite as a propellant, gunpowder was phased out of use.    

Another bas-relief of industrialised munitions work in the 20th century.  The heart of Priddy's Hard in the 20th century was its Laboratory Section, which inspected, repaired, and processed shells, bullets, fuzes, primers, igniters, and detonators.  The depot's finest hour was providing ordnance to forces for the 6 June 1944 D-Day landings during the Second World War, though the facility maintained a key role in supporting the Royal Navy until after the Falklands War in 1982.

A display of ammunition boxes, which replaced the barrel as the all-purpose storage container in the late 19th century.  All but the largest ordnance items were stored in and transported from ordnance depots in such boxes.  Each box is carefully coded with specific colours, letters, and numbers to denote their contents.  The colour indicated the type of ammunition inside, with yellow for high explosive, brown for low explosive, black for armour-defeating, and silver for countermeasures like radar echo (chaff).  The letters represent the origin of the munition, with RNC meaning the Royal Navy Cordite Factory in Holton Heath; CRB meaning Crombie in Scotland; and PHD meaning Priddy's Hard.  Numbers stencilled on the boxes recorded the filling dates and cordite lots, thereby identifying the age of the munition.  Until the 1940s, joiners were employed at Priddy's Hard and other depots to manufacture and repair wooden ammunition boxes; later containers were made from metal.  Packing and unpacking ammunition boxes was the responsibility of different rooms in the Laboratory Sections.  Large shells were packed with wooden fittings to hold them in place, while sensitive detonators were packed in felt-lined boxes, and fuzes and firing tubes were sealed inside tin cylinders to keep out damp.

An assortment of 20th century ordnance, including a 1940-vintage pedestal-mounted Mk II Oerlikon 20mm heavy machine gun; an anti-submarine Burney sweep towed by surface vessels in the First World War; a 1960s-era American Mk 44 lightweight anti-submarine homing torpedo; and a French-designed SS.11 wire-guided air-to-ground missile.   

A high explosive mine disposal charge, part of the Remote Control Mine Disposal System (RCMDS) fitted aboard the Royal Navy's minehunter vessels from the 1980s to 2009.  The RCMDS comprised a small, unmanned submarine (the 'PAP vehicle') controlled remotely and guided by sonar.  The PAP vehicle was deployed from the minehunter and carried countermeasure charges to its target, deploying them and returning to the minehunter to be retrieved.  The high explosive mine disposal charge was used to destroy ground mines on the seabed.  The RCMDS was replaced in Royal Navy Service by the Seafox system beginning in 2007.

An inert training version of the SS.11 missile.  Manufactured by French company Nord Aviation from 1956 to the mid-1980s, the SS.11 was a Manual Command to Line of Sight (MCLOS) wire-guided anti-tank missile that was adapted for naval purposes and could be launched from the Royal Navy's Wessex and Wasp helicopters.  This training missile, a B1 variant with improved electronics, dates from September 1962.  The S.11 missile was in use by the Royal Navy from 1965 to 1980.    

A four-barrelled, 1-inch calibre Nordenfelt machine gun, dating from 1900.  Designed by Swedish engineer Helge Palmkranz in 1879 and financed by the banker and entrepreneur Torsten Nordenfelt, the gun was manufactured by the Nordenfelt Gun and Ammunition Company, with production facilities in Spain, Sweden, and the United Kingdom.  In 1884, a five-barrelled version entered service with the Royal Navy, though some models of Nordenfelt gun featured as many as 12 barrels.  The Nordenfelt gun was eventually outclassed by the Maxim gun.  Ammunition for the Nordenfelt gun was fed into a hopper and carrier block at the rear of the gun, with the gunner using a lever to push the rounds into the barrels; an action block with firing pins for each barrel was then closed and the rounds discharged sequentially.  The gunner then pulled the lever back, releasing the action and carrier blocks, discharging the spent cartridges, and repeated the loading and firing process. 

The gallery devoted to mine warfare at sea.  Examples on display include Mk 5 and Mk 12 ground mines, Mk 17L and Mk 1 buoyant mines, river mines, and Romanian mines.  During the First and Second World Wars, mines were fabricated by Royal Ordnance Factories, though the firing mechanisms were manufactured by private companies.  From 1872, the Royal Naval Armaments Depot Priddy's Hard inspected and repaired mines, which were stored at the facility (until 1920) and on floating hulks moored nearby.  The mine depot at Frater operated between 1918 and 1959, coming under the command of the superintendent of Priddy's Hard from 1935.    

An Mk 1 magnetic mine, widely used by the Royal Navy from 1942.  The first British mine to use the coiled rod, an induction coil that detected the magnetic field of a passing ship, the 500 pounds of explosive held in the mine's central drum would be detonated when the vertical rod running through the drum detected the magnetic field.   

A Second World War Mk 17L contact sea mine, consisting of two 40-inch diameter hemispheres joined by an 8-inch belt.  The Mk 17 mine is fitted with 11 contact horns and a charge of 145 or 204 kilograms (320 or 450 pounds), and could be laid up to 914 metres (2,998 feet) deep.  The mine on display here sits atop its sinker, which would act as the mine's anchor once deployed from a minelaying vessel.  Tethered to its sinker by cable, the mine would float near the surface and detonate when its contact horns were impacted by the hull of a ship or submarine.

Two ground mines: a Mark 12 acoustic/magnetic mine (left) and a sectioned Mk 5 magnetic ground mine (right).  The Mk 5 mine was designed for use against both submarines and surface vessels and could be fitted with either magnetic, acoustic, or a combined magnetic/acoustic firing assembly, depending on the intended application.  The mine's casing was a cylindrical tube 53.3 centimetres (21 inches) in diameter and 2.06 metres (6.75 feet) in length.  The interior of the Mk 5 mines was divided into three sections, with the end sections holding instrumentation and the centre section containing approximately 526 kilograms (1,160 pounds) of Torpex high explosive.   

The laying of mines was done for two purposes.  Defensive minelaying created protective fields, often at natural chokepoints like channels, to defend one's own shipping against enemy attack.  Offensive minelaying was used to sink enemy ships or disrupt enemy shipping routes by laying mines in ambush.  Mines could be deployed by fast minelaying vessels, converted merchant vessels, destroyers, motor boats, submarines, aircraft, and even divers.  In the Second World War, British minelayers laid over 186,000 defensive mines and over 77,000 offensive mines. 

A display of various calibres of naval shells.  Naval ordnance depots like Priddy's Hard would supply Royal Navy warships with their 'authorised outfit' of various types of ammunition.  As the general purpose projectile used by the Royal Navy, High Explosive shells fitted with impact, time, or proximity fuzes use blast effect and high velocity fragments to destroy their targets.  Armour Piercing shells penetrate plate armour before exploding, with the fuze mounted at the rear of the shell in order to withstand the shock of impacting the target.  Anti-Aircraft shells of the heavy category went up to 5.25-inch calibre and could be fired to an altitude of 12,954 metres (42,500 feet), though effectiveness was only greatly increased by the replacement of time fuzes with proximity fuzes.  Star Shells fitted with parachutes were fired high into the sky and served to illuminate or silhouette targets at night with their brilliant magnesium flare.  Radar Echo shells were used to deceive enemy radar systems by releasing a cloud of thin aluminium strips that appear as a solid airborne target on radar screens.      

The name board from HMS Dreadnought (S101), Britain's first nuclear-powered submarine, built by Vickers-Armstrong in Barrow-in-Furness and launched in 1960.  Dreadnought was designed to detect and destroy enemy submarines.  In 1967, she made a round trip between Scotland and Singapore without needing to surface once.  On 3 March 1971, Dreadnought became the first Royal Navy submarine to surface at the North Pole.  She was decommissioned in 1980 due to machinery damage and limited refit facilities then available in the UK for nuclear submarines and remains laid up in Rosyth Dockyard awaiting dismantling and disposal.  

A model of the revolutionary battleship HMS Dreadnought of 1906.  When launched, she was the fastest and best-armed battleship in the world, lending her name as the generic term for an entire generation of battleships.  HMS Dreadnought sported ten 12-inch guns and was powered by new steam turbine engines giving her a top speed of 21 knots (38.89 km/h).  On 29 March 1915, HMS Dreadnought rammed and sank the German submarine U-29, becoming the only battleship to sink a submarine.  Dreadnought was decommissioned in February 1919 and scrapped in Scotland in 1923.

A display of naval gun barrels.  Firing a gun causes wear to the inside of its barrel as a result of friction between the projectile and the barrel's rifling and from the scouring effect caused by exploding propellant.  This wear reduces the accuracy and muzzle velocity of the gun over time.  Because a gun's life could not be predicted simply by the number of shots fired, each gun had to be periodically inspected at armaments depots like Priddy's Hard.  A gun might be fitted to a dozen or more ships over the course of its service life, so a Gun Memorandum followed each gun from ship to ship, recording the inspections performed.  Guns and breeches 'condemned' as too badly worn from firing to continue in service were removed to a gunwharf for repair or relining.  Priddy's Hard had workshops, blacksmiths, sheet metal shops, a foundry, and a small arms test range to carry out this work.  The depot's Stores Section held gun spares and other non-explosive stores, while guns were stored on the outdoor Gun Ground, serviced by a giant overhead gantry crane.          

A Quick Firing (QF) 4.7-inch naval gun in single mounting.  This gun was the standard armament on Second World War Royal Navy destroyers.

A Bofors 40mm Mk N1 gun on a Mk 7 mounting.  Swedish designed, the Bofors gun was widely used from 1942 to defend naval ships against aircraft.  Smaller vessels, such as armed motor boats, also used the Bofors gun against surface targets.  Capable of firing up to 120 rounds per minute, the Bofors gun was fed with clips of four rounds apiece. 

A view of the gallery devoted to the history of naval guns.  The room is dominated by several long gun barrels of various calibres.

A Hotchkiss Quick Firing (QF) 3-pounder gun on a high angle mounting.  Adopted by the Royal Navy in the 1890s, the Hotchkiss 3-pounder gun was used to defend against small, fast-moving torpedo boats.  The gun displayed here was adapted for anti-aircraft use in the Second World War through the addition of a shield and a contemporary anti-aircraft gun sight, as well as the ability to elevate 50 degrees.  With a pressing need to equip warships and merchant vessels with anti-aircraft guns when war broke out in 1939, old guns like the Hotchkiss were used until replaced by more modern weapons, such as the automatic 20mm Oerlikon or 40mm Bofors guns.  Neverthless, Hotchkiss 3-pounder guns continued to be used until recently for ceremonial purposes.     

The breech from a 15-inch naval gun, dating from 1914, which once equipped a battleship of the Queen Elizabeth class.  This item is on loan to the Museum of Naval Firepower from the National Maritime Museum in Greenwich.

A builder's model of the 28,600-ton, 14-inch gun armed 'super-dreadnought' HMS Canada, originally ordered from Britain's Armstrong Whitworth yard by Chile as the Almirante Latorre.  The ship was instead purchased by the British government when the First World War broke out and was re-named HMS Canada.  She was commissioned into the Royal Navy in September 1915 and served in the Grand Fleet, taking part in the Battle of Jutland the next year.  Sold to Chile after the war for a fraction of her original construction cost, the Almirante Latorre served as the Chilean Navy's flagship and was only scrapped in 1959.

A 4-inch Mk 23 submarine gun on an S2 mounting, originally fitted to the Amphion class submarine HMS Andrew.  Introduced into service in 1945, the Mk 23 gun was the last type of gun to be installed on Royal Navy submarines, serving until 1974.  The Mk 23 gun could fire a 16.24 kilogram (35.81 pound) shell at a rate of 15 shots per minute, though most submarine surface gun engagements were of short duration and against merchant vessels or shore targets due to the extreme vulnerability of the submarine to counterattack.

The Oerlikon 20mm/85 KAA gun on a manually-controlled GAM-BO1 mounting.  Manufactured by the British Manufacture and Research Company (BMARC) and introduced around 1985 as a result of increased interest in light machine guns following the Royal Navy's experience in the Falklands War, the 20mm/85 gun replaced the Second World War era 20mm Oerlikon gun for use against small boats, shore targets, and light aircraft.  The gun could depress to -10 degrees and had a maximum elevation of +55 degrees, with a rate of fire of 900-1,000 rounds per minute.  Its effective range against surface targets was 2,000 metres (6,562 feet) and 1,500 metres (4,921 feet) against airborne targets.  This 20mm/85 gun was fitted to the Invincible class aircraft HMS Ark Royal and was the last gun fired on the ship before it decommissioned in 2011.  Also fitted to Type 42 destroyers, Type 22 frigates, and Batch 2 and 3B Leander class frigates, the 20mm/85 gun was retired from Royal Navy service in 2016.

Another view of the naval gunnery gallery.

A model of the Dutch-designed Goalkeeper close-in weapon system (CIWS), designed as a last line of defence against incoming missiles and aircraft.  The system comprises a Gatling gun mounted on the deck, served by a control system below deck.  When activated, Goalkeeper automatically seeks, detects, and destroys targets.  The Goalkeeper system was in use aboard Royal Navy ships from 1980 to 2016.

A Goalkeeper close-in weapon system control console, at which an operator would sit to monitor information on targets received by Goalkeeper's search radar and control system.  Multiple targets could be monitored simultaneously, with the operator capable of overriding the system to change the priority of attack by the system's automatic Gatling gun.

A gallery devoted to anti-submarine weapons, from depth charges to ahead-throwing mortar systems.

A Mk 4 depth charge thrower with a Mk 7 depth charge.  The depth charge was launched from a surface ship by firing a cartridge on the thrower which propelled upward the cradle holding the depth charge.  Hurled into the air away from the ship, the depth charge would detonate after sinking underwater to a pre-set depth.  Each depth charge thrower was crewed by a team of five men, each with a specific duty who worked to a set drill, like a gun's crew.  A tiered rack of charges was developed which improved the speed of re-loading.  The Mk 4 depth charge launcher entered service in 1940.     

A Hedgehog anti-submarine mortar projectile.  The Hedgehog was the first ahead-throwing anti-submarine weapon deployed by the Royal Navy, being installed aboard warships from 1942 onwards.  The system consisted of a metal box mounted forward of the ship's bridge and containing 24 spigot-mounted high explosive mortars.  Ahead-throwing weapons allowed the attacking surface ship to maintain sonar contact with the target submarine during the attack, thereby increasing the probability of a hit.  Additionally, as Hedgehog mortars only exploded on contact with the submarine's hull, a successful attack was more readily apparent compared to the earlier drum-type depth charges fired off the sides and stern of a warship.  Typically a volley of Hedgehogs would be fired in a box pattern to improve the chances of a 'kill'.    

A Squid anti-submarine mortar launcher.  Developed in 1943 to replace the earlier Hedgehog anti-submarine mortar, the Squid was another ship-mounted ahead-throwing weapon, but one which fired a much heavier mortar.  The Squid's three barrels were angled slightly to deploy their mortar bombs in a triangular pattern 250 metres (820 feet) ahead of the firing ship.  Most Squid-equipped ships were fitted with two triple-barrelled launchers which were fired in salvo to create two three-charge patterns 7.6 metres (25 feet) above and below the submarine target, respectively; trapped in between the two patterns, the submarine's hull would be crushed by the pressure wave.  Studies proved that Squid was nine times more effective than traditional drum-type depth charges.  Rushed into service at the height of the Battle of the Atlantic, the Squid mortar was eventually installed on 70 Royal Navy frigates and corvettes and was credited with 17 submarine kills in 50 attacks.  The Squid system was retired in 1977 and replaced by the Limbo mortar system.

A 305mm (12 inch) Squid mortar bomb on its loading trolley.  The mortar tubes were rotated sideways to allow the bombs to be pushed from the trolley into the tubes and then rotated into an upright position before firing.  The range and bearing of the submarine target were plotted by the ship's sonar and the Squid mortars were automatically fired at a range of 366 metres (1,200 feet).  Each Squid mortar bomb weighed 177 kilograms (207 pounds) and contained an explosive charge of 94 kilograms (207 pounds).  The mortars were effective to a depth of 274 metres (900 feet), detonating according to a pre-set clockwork time fuze.

The sole surviving example of a Fairlie mortar, a long-range depth charge thrower prototype developed by John I. Thornycroft Ltd in 1941 under contract with the Admiralty.  Five such throwers were manufactured by Thornycroft, featuring a bronze alloy base and a tube of rolled boiler plating.  The 50 degree angled tube could throw a depth charge about 302 metres (991 feet) using a cordite charge of 16 ounces.  The five examples built by Thornycroft were used for trials aboard the W-class destroyer HMS Whitehall in July 1941.  Whitehall's forward gun was removed and the depth charge throwers installed on the ship's forecastle.  Although relatively successful, the Admiralty decided not to proceed with the Fairlie mortar design after concluding that the Hedgehog mortar, also under development at the time, would be a more effective anti-submarine weapon.  

The gallery showcasing the history and development of the torpedo.  Examples on display include the American-designed Mk 11 torpedo, in service between 1926 and 1945; the German 'Neger' manned torpedo-carrying craft used by the Kriegsmarine between 1943 and 1945; the Mk 24 Tigerfish heavyweight acoustic homing torpedo used by the Royal Navy between 1979 and 2004; and the Sting Ray lightweight acoustic homing torpedo currently in Royal Navy service.  

Another display of historic torpedoes, including a 21-inch Mk VIII torpedo (top rear, with orange nose); a German-designed Schwartzkopff torpedo from 1873 (top front); the experimental HEYDAY rocket-propelled torpedo developed by famous British designer Barnes Wallis in the 1950s (bottom front, silver); and an early version of the Whitehead torpedo, dating from around 1872.

A bust of Robert Whitehead (1823-1905), the British inventor of the first effective self-propelled torpedo.  In the 1850s, Whitehead was managing a company in Trieste, on the Adriatic coast, making steam boilers and engines.  After meeting Giovanni Luppis, a retired Austro-Hungarian naval officer and inventor of the first self-propelled torpedo, Whitehead developed Luppis's design to produce a ship-launched torpedo capable of maintaining a straight trajectory to its target using internal devices to maintain a constant depth and direction.  The torpedo was driven by compressed air supplying a two-cylinder cycle motor.  Whitehead's company, based in Fiume, led the world in torpedo design prior to the First World War.

An inert training version of the WE.177 nuclear bomb, Britain's longest-lived free-fall nuclear weapon, which remained in Royal Navy and Royal Air Force service from 1966 to 1998.  The WE.177 was adapted to be dropped from 18 different types of aircraft and helicopter and replaced all previous types of free-fall nuclear bombs in the UK's arsenal.  Although originally developed as a tactical nuclear weapon, the WE.177 was initially carried by the Royal Air Force's V-bomber force in the strategic role as a 'lay-down weapon', with the bomb's descent slowed by a parachute in order to provide the bomber aircraft sufficient time to get to a safe distance before the bomb's detonation.  The Type A model of the WE.177 weighed 272 kilograms (600 pounds) and was a low-yield (10 kiloton) weapon dropped from naval strike aircraft or helicopters.  The Type B model of the WE.177 was longer and heavier, weighing 457 kilograms (1,010 pounds), and had the largest yield of 450 kilotons, equivalent to thirty times the power of the atomic bomb dropped on Hiroshima in 1945.  The Type C model of the WE.177 was similar in size to the Type B model but possessed a lower yield of 200 kilotons.         

A quadruple Seacat Mod 0 short-range surface-to-air missile launcher and inert training missiles.  Designed by Short Brothers and introduced into Royal Navy service in 1962, Seacat was the first naval surface-to-air missile for close-range air defence and was based on an anti-tank missile design.  The Seacat replaced anti-aircraft guns, such as the 40mm Bofors, and was a popular export to other other countries, eventually being adopted by 22 foreign nations.   Early versions of Seacat, such as the Mod 0, required an operator to track the bright flare of the missile tail through sighting binoculars and send radio guidance commands to the missile using a joystick, with the signals transmitted via an aerial on top of the Seacat launcher.  Featuring an 18 kilogram (40 pound) warhead, Seacat missiles fired from Royal Navy warships downed a number of Argentine aircraft during the 1982 Falklands War; however, the increasing prevalence of supersonic, sea-skimming missiles rendered the manually-controlled, subsonic Seacat obsolete and the system was retired from Royal Navy service in the 1980s, being replaced by the longer-range, sea-skimming, supersonic Sea Wolf missile system.    

A Red Top air-to-air missile, designed by Hawker Siddeley and introduced to service in 1964.  The Red Top was carried by the de Havilland DH.110 Sea Vixen fighters of the Royal Navy's Fleet Air Arm, which were retired from service in 1972; however, the Red Top continued to arm the English Electric Lightning fighters of the Royal Air Force until their retirement in 1988.

A display of missiles and rockets once used by the Royal Navy, including the sea-skimming, short-range anti-ship Exocet missile (1973); the AIM-7 Sparrow medium-range air-to-air missile (1968); the AIM-9B Sidewinder air-to-air heat-seeking missile (1956); the Australian-developed Ikara long-range anti-submarine torpedo delivery missile (1960); the Sea Skua short-range, helicopter-launched anti-ship missile (1982); and the Firestreak close combat, air-to-air heat-seeking missile (1954).   

The remains of the main tail section of Sea Dart surface-to-air missile JZ 391, fired in May 1982 by the Type 42 destroyer HMS Coventry.  During the Falklands War, Coventry shot down two Argentine A-4 Skyhawk fighter-bombers and an SA 330 Puma helicopter using Sea Dart missiles before being itself bombed and sunk by a pair of Argentine Skyhawks on 25 May 1982.  The tail section of JZ 391 was found and recovered from the peat on East Falkland in July 1983 and returned to the UK aboard one of Coventry's sisterships, HMS Southampton.     

The barrel-vaulted brick ceilings of the interior of the Grand Magazine, the original gunpowder storage magazine at Priddy's Hard, completed in 1777.  Gunpowder is labelled a 'low explosive', not being highly sensitive to shock or friction and requiring flame or heat to ignite.  The magazines at Priddy's Hard were cool, dim, dry, clean, and tightly-regulated to ensure safety.  Today, the Grand Magazine no longer stores powder and can be rented as a  unique venue for weddings and other events.

A display of some of the equipment used by workers at Priddy's Hard during the Second World War.  The high point of Priddy's Hard's war experience was the production of thousands of tons of ammunition for Operation Neptune, the naval component of the 6 June 1944 D-Day landings.  In addition to filling and assembling thousands of shells, Priddy's Hard also prepared 30,000 5-inch rockets for use by rocket-armed landing craft assigned to bombard the French coast during the amphibious landings.  During the Second World War, Priddy's Hard employed 2,500 women, some of whom were as young as 16 even though the official minimum age was 18.  Although they received better pay than jobs in other industries, women at Priddy's Hard still earned less then men and no female employees were ever promoted to the role of foreman, a job restricted solely to men. 

Another view of the interior of the Grand Magazine, which could house 6,200 barrels of volatile gunpowder in neat stacks within its thick walls.

The café, located at the end of the tour route, provides visitors with an opportunity to enjoy a hot beverage, snack, or light meal before departing.  A patio open during pleasant weather sits adjacent to Portsmouth Harbour.