‘Collapsible trunks forming escape locks when submarine’s compartments are flooded’.
This is an illustration of a very useful invention used aboard early Royal Navy submarines. The following text is taken from Davis’ book, “Most of the Submarines of the Royal Navy are provided with collapsible trunks fitted water-tightly to certain hatches. They are conveniently stowed, ready for instant use and take up very little space in the compartments…. When required for use in an emergency, it is pulled down and secured, the submarine compartment is flooded, air trapped in the trunk is released by the opening of a valve, and the hatch is opened.” This illustration was no doubt used in the training of Royal Navy submarine recruits.