World War I The deck gun was introduced in all submarine forces prior to
World War I. However, it came to the fore in the German navy, and proved its worth when
U-boats needed to conserve
torpedoes or attack enemy vessels straggling behind a
convoy. Submarine captains often considered the deck gun as their main weapon, using much more expensive but not always accurate torpedoes only when necessary or advisable (as a deck gun necessarily revealed a submarine's position, whereas a torpedo could be used either under water or effectively at night). In addition, submarines carried many more gun rounds than torpedoes - ten or fewer during World War I, fired in spreads of multiple warheads to increase the likelihood of a successful hit. An example of this approach was
Lothar von Arnauld de la Perière, who used a deck gun or a dynamiting team on 171 of his 194 sinkings. The Royal Navy tried an innovative approach in World War I with its three
M-class submarines, which mounted a single
12 inch (305 mm)/40 caliber naval gun intended to be fired while the submarine was at
periscope depth with the muzzle of the gun above water, principally in a
shore bombardment role. This design was found unworkable in trials because the submarine was required to surface to reload the gun, and problems arose when variable amounts of water entered the barrel prior to firing.
World War II The French submarine was
launched in 1929 with two
203 mm/50 Modèle 1924 guns in a
turret forward of the
conning tower. These were the second largest guns carried by any submarine after the British during the
Second World War. The
London Naval Treaty of 1930 restricted submarine guns to a maximum of 155 mm (6.1 inches). In the early part of
World War II, German submarine commanders favored the deck gun for similar reasons as their World War I counterparts; the limited number of torpedoes that could be carried, the unreliability of torpedoes, and because their boats could only travel submerged at slow speed for short distances. The deck gun became less effective as convoys became larger and better equipped, and merchant ships were armed. Surfacing also became dangerous in the vicinity of a convoy because of improvements in radar and direction finding. (See
Defensively equipped merchant ships (DEMS) and
United States Navy Armed Guard). German U-boat deck guns were eventually removed on the order of the supreme commander of the
U-boat Arm (
BdU) during World War II, and those deck guns that remained were no longer manned. For a few months in 1943, some U-boats operating in the
Bay of Biscay were equipped with
enhanced anti-aircraft guns (at the trade-off of reduced torpedo loadouts), being known as "U-Flak" boats to be deployed as service escorts for regular U-boats. After the
Royal Air Force modified their anti-submarine tactics which made it too dangerous for a submarine to stay on the surface to fight, the U-Flaks were converted back to standard U-boat armament configuration. Japanese
submarine cruisers used
14 cm/40 11th Year Type naval guns to shell
California,
British Columbia and
Oregon during World War II. Two notable deck guns from German U-boats used in
World War II were the
SK C/35 (not to be confused with
8.8 cm Flak) and the
SK C/32. The 88 mm had ammunition that weighed about and was of the projectile and cartridge type. It had the same controls on both sides of the gun so that the two crewmen that were in charge of firing it could control the gun from either side. The 105 mm evolved from the 88 mm in the sense that it was more accurate and had more power due to the ammunition it fired. In the
US Navy, deck guns were used through the end of World War II, with a few still equipped in the early 1950s. Many targets in the
Pacific War were
sampans or other small vessels that were not worth a torpedo. The unreliability of the
Mark 14 torpedo through mid-1943 also promoted the use of the deck gun. Most US submarines started the war with a single
3-inch (76 mm)/50 caliber deck gun, adopted in the 1930s to discourage commanders from engaging heavily armed escorts. However, the aging
S-boats were equipped with a
4-inch (102 mm)/50 caliber gun, which was often used to re-equip 3-inch-gunned submarines as the S-boats were transferred to training duties beginning in mid-1942. By 1944 most front-line submarines had been refitted with a
5-inch (127 mm)/25 caliber gun, and some were equipped with two 5-inch guns. The
cruiser submarines , and were each fitted with two
6"/53 caliber guns Mark 18 (152 mm) as built in the 1920s, the largest deck gun to be fitted on any United States submarine. In the
Royal Navy, the was the last British submarine to be fitted with a deck gun (a
QF 4 inch Mk XXIII). HMS
Andrew was
decommissioned in 1974 and the deck gun is now in the
Royal Navy Submarine Museum. The last submarines in service in any navy to mount a deck gun were two of the four s of the
Peruvian Navy in 1999. ==See also==