A roll film negative. On board the submarine Sealion (1959) towards the end of a long refit at Portsmouth. The photographer is in the forward torpedo compartment looking forward and down at the dome bulkhead at 16 station from the port side of the torpedo tubes at 20 station. A gauge on the left is labelled 'fluid regulator setting' and an electrical box on the right is labelled '778 CCB deep transducer'. A vertical format negative.