History 1: Building the A7
This is a very condensed version of the story, the full tale of the design and building of HM Submarine A7 can be found in the Project Report.
The A7 was a Royal Navy A-Class coastal submarine that was laid down in September 1903 and completed in April 1905 as part of the Group II programme that included submarines A5 to A13. Like all her class, she was built by Vickers in Barrow-In-Furness as a joint development between the company and the Admiralty; the technology was new and the A class were the first British designed submarines in the Royal Navy. The first of the new design, the 100 ft. long, 165 ton submarine A1 was laid down in February 1902 and was launched in July the same year.
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HM submarine A7 (Lawrence Collection)
With A1 being very much a prototype, the first batch of true A class submarines A2-A4 were launched in June and July 1904; these included a significant number of design improvements over the original A1 including a modified hull shape, a taller conning tower, twin torpedo tubes and an improved petrol engine. The design also included a second watertight hatch at the bottom of the conning tower, a design improvement added after the ramming and sinking of A1 by the mail steamer Berwick Castle in March 1904. The usefulness of the lower hatch was tested in anger in 1906 when sister-boat A9 was rammed, her conning tower was holed and she had to surface with a conning tower full of water.
The third batch of A class boats, known as Group II and including submarines A5 to A12, were launched between February and September 1905. This new batch contained yet more improvements, with a better engine, a new layout for the ballast tanks, a different arrangement for the engine exhaust and a taller conning tower. A7 was laid down at Vickers yard on 1st September 1903 as yard number 305, launched on 23 January 1905 and completed on 13th April that same year with pennant number I.17. The A7 was 30.2m (99ft) long with a beam of 3.9m (12ft 9in) and a depth of 3m (10ft) and displaced 190 tons on the surface and 205.5 tons submerged. On the surface she was powered by the latest version of the Wolseley petrol engine and submerged she was powered by a 150 h.p. electric motor fed by a large bank of batteries. The petrol engine could push her along at 12 knots (22.2 kmh-1) on the surface and give her a range of 500 nautical miles but submerged she could only achieve 8 knots and a range of 30 miles. The A7 was armed with two 18in bow mounted torpedo tubes and she had a crew of 11. Bilge keels were fitted along a quarter of the length of the outside of the hull, 9in (230mm) broad and at an angle of 49° to the vertical, so the hull did not tend to roll even when the sea was rough. The last of the class was A13 launched in 1905 but not commissioned until 1908; A13 was notable as she was the first Royal Navy submarine to be fitted with a diesel engine.
Plans of the submarine A13 (BAE Systems Archive)
The operational diving depth of the A Class was 15m (50ft) with a maximum depth rating of just 30m (100ft). A deeper diving depth would have required a thicker pressure hull which would add more weight to an already overweight design, so a bigger hull would be needed which would displace more water to compensate. The very narrow operating range did not allow much of a margin for error in a class of small submarine that was renowned for taking unprompted dives towards the seabed. The submarine itself was also 30m long so a steep dive at the operating depth could soon put the bow of the submarine below the maximum rated depth before the dive could be brought under control.
Early in 1905, the A7 became the first Royal Navy submarine to be fitted with experimental hydroplanes on the forward side of her conning tower. Each plane was ten square feet in area actuated from the control room by a rod connected to gearing on the plane shaft. Initially this class of submarine was dived while stationary in the water but later it was found that they could
submerge while underway and the conning tower hydroplanes were added to see if this would assist in diving. The experiments were not a success and the hydroplanes were later removed.
This is a very condensed version of the story, the full tale of the design and building of HM Submarine A7 can be found in the Project Report.
