One diver is helped into his enormous and weighty boots and looks none too thrilled at the prospect of entering the tank.
Meanwhile, a previous ‘contestant’ gazes out from the bottom of the chamber through the windows of his helmet.
This Stephen Cribb photograph was taken in either 1907 or 1908 when the Royal Navy’s diving tank was situated at Whale Island in Portsmouth Harbour.
Training for divers was carried out there before it moved to HMS Vernon, now Gunwharf Quays.
The second picture today shows Holland 3, a submarine launched on May 9, 1902, in Portsmouth Harbour later that year.
The boat was designed by Vickers at Barrow-in-Furness, laid down on February 4, 1901, and commissioned on August 1, 1902.
Holland 3 sank in trials in 1911 and was then sold on October 7, 1913.
And finally...you might never have seen a fleet review quite like this.
Apparently the submarine service was a little miffed at not being included in the Spithead home fleet review of August 1907.
So Edward VII invited the entire submarine fleet to gather for a review of their own in 1908.
And here they are – 35 boats moored off Fort Blockhouse, Gosport, in Portsmouth Harbour in this 1908 photograph, again by Stephen Cribb.