A sheet 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 from the centreline at 78 station showing the Caird & Rayner Ltd distilling plant type 'D'. At the top of the picture is the pipework under the two 16 cylinder Admiralty Standard Range diesel engines. A hinged drop-down front locker is on the left. An Admiralty copy negative of an Admiralty photographic print. A vertical format negative.