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 from 79 station on the centreline showing the closed watertight door in the bulkhead at 77 station. The ballast pump starter panel is on the left and the oil fuel separator is on the right. Warning lamp panels for Nos. 1 and 2 distillers are above the door. 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 to starboard of the watertight door. 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.