When the Scorpion is strafed by Bf109's, Travis points an automatic pistol at the Captain. The weapon is clearly a Colt .45 M1911A1. The standard RN sidearm in 1981 was the 9mm FN Browning Hi-Power.
Both the Colt and the Browning were used by British forces during WW2; however, before leaving on its mission, the recovered submarine would have been issued with modern small arms.
HMS 'Scorpion' is supposed to be a British submarine, presumably (given her name) an S-Class. However, she doesn't resemble any Royal Navy submarine of the Second World War, looking far more like a late-war German Type VIIC U-boat. The only significant concession is that exterior periscopes have been altered to give it a more British look, but they are closer to what was on a T-Class submarine than on the S-Class.
Submarines of the WW2 era didn't have the now-familiar rotating radar on a circular display.