Ordnance QF 4 inch gun Mk XXIII
Mk XXIII gun from HMS Andrew at the Royal Navy Submarine Museum, Gosport.
Type	Submarine deck gun
Place of origin	United Kingdom
Service history
In service	1945-1974
Used by	United Kingdom
Wars	Indonesia–Malaysia confrontation Cold War
Production history
Produced	1945-46
No. built	31
Specifications
Mass	1,568 lb (711 kg) barrel and breech
Length	137.6 in (3.495 m)
Barrel length	132.2 in (3.358 m) bore (33 calibres)
Shell	Fixed QF 35 lb (15.9 kg) 38.5 lb (17.5 kg)
Calibre	4 in (102 mm)
Breech	horizontal sliding-block
Carriage	Submarine SII mounting
Elevation	-5 to +30 degrees
Traverse	360 degrees[1]
Rate of fire	about 15 rounds per minute
Muzzle velocity	35 lb: 1,791 ft/s (546 m/s) 38.5 lb: 1,745 ft/s (532 m/s)
Maximum firing range	12,080 yd (11.05 km) 35 lb HE shell at 30 degrees:

The QF 4-inch gun Mark XXIII was introduced in late 1945 as a deck gun for Royal Navy submarines. It was the last type of gun to be fitted to British submarines, finally being retired in 1974.

Development and service

Development of the Mark XXIII began in 1942, as a lighter replacement for the QF 4-inch gun Mark XXII, which was based on a gun introduced in 1911. It was too late to see service in World War II, but was fitted to Amphion-class submarines that completed after October 1945.^[2] It was also fitted to some T-class submarines.^[1]

Between 1955 and the early 1960s, the Amphion-class boats were modernised with new streamlined conning towers and casings. This work included the removal of the deck gun, although the underlying supports for the gun mountings were retained in case they were required. This facility was put to use during the British involvement in the Indonesia–Malaysia confrontation from 1962 to 1966, when the flotilla of Amphion-class submarines which were deployed in the conflict were again fitted with Mark XXIII guns. These were used to counter blockade-running Indonesian junks and other small vessels.^[3] HMS Andrew retained her gun into the 1970s; the last firing was on 2 December 1974.^[1]

Surviving examples

HMS Andrew's Mark XXIII gun is preserved at the Royal Navy Submarine Museum, Gosport.^[4]