gun crew was provided as built due to weight restrictions, except on Tabard, Talent, and Teredo. Many other T-class boats received improvised gun shields manufactured by depot ships in the Far East, providing some degree of protection. The gun had a crew of five, and T-class submarines were initially allocated with 100 rounds of ammunition for the 4-inch gun. This proved insufficient and was soon increased; by the end of the war, T boats would often not carry reload torpedoes in favour of taking more gun ammunition. The standard anti-aircraft armament carried by T-class submarines was three .303-inch machine guns. These were initially Lewis guns, but from 1941 onward replaced with the better Vickers gas-operated (VGO) machine gun. The Vickers was sometimes substituted with the Bren gun if supplies could be spared from the Army. Later, most T-class boats were retrofitted or completed with the ubiquitous 20 mm Oerlikon. This was located aft of the conning tower. Most T-class boats were fitted with only one, but Tantivy carried two 20 mm cannon side by side on pedestal mountings, while Tireless was completed with a twin Oerlikon Mark 12A mounting. The crew of Terrapin was able to acquire a .50 inch Browning air-cooled machine gun on their own initiative, but this weapon was too powerful for the conning tower's brass structure, and was eventually dropped. Service history Prewar The lead boat of the class, Triton, was commissioned on 9 November 1938. She would be joined by another 14 T-class submarines ordered under the prewar 1936–1938 Programmes. The unfortunate loss of Thetis on 1 June 1939 along with 99 of the men on board during her trials led to modification of the Royal Navy's submarine escape procedures. Triton was the only member of the class to undergo full trials, for the outbreak of war meant that the Royal Navy could not afford this luxury at a time when modern submarines were desperately needed. When war broke out on 1 September 1939, there were only three T-class boats in service: Triton, Triumph and Thistle. Second World War As the Royal Navy's standard ocean patrol submarine, the T-class submarines were heavily engaged during World War II, from the North Sea to the Mediterranean, and finally the Far East. The nature of the British submarine campaign against Germany during the early stages of the war was very different from that of the German submarine campaigns