is it a seahorse nursery sandpit
Stackable, fold-away bunks for RMs ( SBS? ) embarked on one or other of HM's untersee boats.
Bunks to fit on submarine torpedo stowage racks.
Its the correct answer; as there are no spare bunk spaces on a submarine, and even when fully bombed up, you leave a space or two on the racks so that you can shuffle the various torpedos and missiles around to load your chosen armament into the tubes, then these spare spaces in the racks are fitted with trays with mattress for 'spare people' to sleep in. My only memory that I will admit to publicly is that, because its an ordnance space, and therefore nor heated, its jolly cold.
I don't think I have broken the official secrets act with any of the above...
[B][I]Wishing things away is not effective.[/I][/B]