A roll film negative. On board the submarine Sealion (1959) towards the end of a long refit at Portsmouth. The photographer is in the generator room below the main flat between 77 and 82 stations, this space being irreverently known as the snake pit. He is looking aft along the trench under the main flat from the centreline at 81 station showing the lower part of the port and starboard 16 cylinder Admiralty Standard Range diesel engines. A number of handwheel valves are in the foreground. A vertical format negative.