On board the submarine Walrus (1959) alongside the fitting out berth at Scott's Shipbuilding & Engineering Co Ltd shipyard at Greenock, on the Clyde. The photographer is in the main generator room between 77 and 92 stations on the main flat looking forward and to starboard from 81 station on the centreline showing the Reavell H.P. air compressor and the oil fuel separator with a vertical screen which is marked "This screen not to be moved without Admiralty approval". Against the starboard side of the boat are a battery vent trunk, a gauge board with seven levers and a Waller compressor starter. Nine terminal boxes, six valve handwheels, two of which marked for O.F. snap tanks, and a vertical gauge for the snap tanks are against the forward bulkhead. The snap tank is used to give a rapid measurement of the fuel consumption of one engine. This can he ascertained after noting the time taken by the engine to consume a small quantity of fuel, approximately 1 gallon. The fuel level in the tank is indicated by a gauge glass and restriction plates in the tank mark the beginning and end of each calibrated section. The positions of these plates are marked of on a level indicator, mounted alongside the gauge glass.