The Mersey-class HMS "Forth" with its flotilla of submarines.
From a postcard.

Her commanding officer in 1905 was Commander Sydney S Hall and in command of the submarine flotilla was Lieutenant Algernon H C Cundy.

Accidents to the submarines were commonplace.  "A-9" came into collision with the coaster "Coath" in Cawsand Bay on February 13th 1906.  She was not much damaged and the crew were uninjured so she was able to make her own way back to the depot ship.  The photograph below shows her and "A-7" alongside HMS "Forth" on February 14th, when the damaged casing enclosing the conning-tower had been removed and the bent periscope was being hoisted out.

Submarines "A-7" and "A-9" alongside HMS "Forth" on February 14th 1906.
©  Illustrated London News.

More serious was the sinking of "A-7" on January 16th 1914 during a training exercise in Whitsand Bay, with the loss of 2 officers and eleven ratings.

HMS "Forth" was expected to be renamed HMS "Howard" but instead she was withdrawn and sold for scrap in 1921.

What was to become the next HMS "Forth" was laid down in June 1937 at the Clydebank Yard of Messrs John Brown and Company, from which she was launched on August 11th 1938.  She was a sister ship of HMS "Maidstone".  Measuring 574 feet in length overall, she displaced some 8,000 tons and was manned by a crew of 502 officers and ratings.  her engines of 7,000 shaft horse-power gave her a top speed of 17 knots.  She was very well armed for a British depot ship: eight 4.5 inch guns, four 3 pounders and six small guns.

HMS "Forth" arrived at Devonport on Sunday May 14th 1939, so the Western Morning News reported, and went up harbour to numbers 2 and 3 jetties in the Royal Dockyard to prepare for replacing HMS "Lucia", a former German liner captured by HMS "Berwick" in September 1914, as the Depot Ship of the Second (Home Fleet) Submarine Flotilla, which was based at Devonport.  She was commissioned on May 12th 1939 and her commanding officer was Captain W D Stephens.

In August 1939 HMS "Forth" set sail for Dundee, Rosyth, Holy Loch and eventually Halifax, Nova Scotia.  She did not return to Devonport until November 1960but then went to Chatham for a refit.  She finally arrived back in Devonport on January 14th 1972 and was re-commissioned on February 15th 1972 as HMS "Defiance", Fleet Maintenance Base and 2nd Submarine Squadron Depot Ship.  She was paid off on April 21st 1978 and the staff moved ashore to HMS "Drake".  HMS "Forth" was finally broken up in 1985.