QF 4.7 inch Mark XI gun

QF 4.7 inch Mark XI
Forward turrets on HMS Matchless
Type	Dual-purpose gun
Place of origin	United Kingdom
Service history
In service	1941-1970
Used by	Royal Navy Turkish Navy
Wars	World War II Korean War
Production history
Designed	1937–39?
No. built	87
Specifications
Weight	3.351 long tons (3,405 kg)
Length	247.7 in (6.29 m)
Barrel length	Bore: 236.2 in (6.00 m) L/50 (cal)
Shell	Separate-loading
Shell weight	62 pounds (28.1 kg) SAP or HE
Calibre	4.724 inches (120.0 mm)
Breech	Semi-automatic horizontal sliding-block
Recoil	Hydro-pneumatic
Elevation	-10° to +50°
Rate of fire	10 rounds per minute
Muzzle velocity	2,538 ft/s (774 m/s)
Maximum firing range	21,240 yards (19,420 m) at 45°

The 4.7 inch QF Mark XI was a 50-calibre, 4.7-inch (120 mm) naval gun deployed on Royal Navy (RN) and Allied destroyers during World War II.

The QF 4.7-inch Mk XI gun, on the Mk XX twin mounting, was introduced to the RN aboard the L and M class destroyers, in commission from 1941 onwards. It featured a 62 lb (28.1 kg) shell fired at 2,538 ft/second (774 m/s) to a maximum range of 21,240 yards (19,420 m) at 45 degrees of elevation. The Mk XX mounting was fully enclosed, but the hoists did not revolve with the turret. The gun's firing cycle was six seconds and the separate shell and cordite hoists for each gun provided shells and cartridges at a rate of 10 per minute. The shells and cartridges were transferred from the hoists to the tilting tray of the fuze-setting machine by hand. Once the fuzes were set, they slid forward to the loading tray from which they were rammed forward into the breech by a hydraulic rammer. The horizontal sliding-block breech opened semi-automatically after the guns fired.

The guns could be loaded at any angle of elevation. The Mk XX mounting could elevate to a maximum of 50° and depress to −10°. The turret had a maximum powered training rate of 10° per second, but was manually elevated. Including the crew and ammunition, the revolving weight of the mounting was 37.363 long tons (37.963 t). It was protected by a gun shield .25 inches (6.4 mm) thick., too thin to hold a direct hit, but still appreciable versus small splinters, explosions, small caliber rifles.

With a shell 24% heavier, the new gun was far more powerful than the previous 45 calibre long 4.7 inch gun making it a match for a weapon such as the Italian 120/50 mm, whilst also improving the air defence role. It could now penetrate 3 inches (76.2 mm) of armour at a range of 10 km rather than 5.9 km. In the Battle of Pantelleria on 15 June 1942, HMS Marne, Matchless and HMS Ithuriel engaged a superior Italian task force. Marne fired 704 shells, Matchless 746 shells, while Ithuriel (with four 4.7 /45) managed to fire only 246 shells. Marne hit the cruiser RN Eugenio di Savoia with a single shell at around 5.50 AM. Matchless failed to hit the other cruiser, RN Montecuccoli, but later hit the large destroyer Ugolino Vivaldi. The new 120/50 mm shell was heavy and powerful, and the Italian destroyer was soon lying dead in the water, with a furious fire at midship. That destroyer was saved only towing her to a near naval base, where the fire was finally extinguished.