The two ‘large light cruisers’ were also assigned above-water tubes, which were ordered in 1916 for delivery in August and September 1917. Initial proposals called for two single fixed tubes on each side, later reduced to a single tube. In April 1917 CO of Glorious asked for the battery already approved for light cruisers, two triples on each side. In the light cruisers it was justified on the grounds that they might find themselves in an advantageous attack position during a fleet engagement. The much faster ‘large light cruisers’ could do even better. The CO of Furious made a similar proposal and CO of the battlecruiser force (Rear Admiral Pakenham) agreed. Triple tubes would replace the two singles already approved. DTM argued that triple tubes would make for a crowded and vulnerable arrangement. DNC suggested that the tubes be worked into the ship’s side, hence both free of gun blast and widely separated. In June 1917 DTM suggested installing the tubes already on order abreast ‘Y’ barbette and new tubes when delivered fitted in the approved covered space, giving each ship a total of four above-water tubes. As for triple tubes, DNC pointed out that in Glorious and Courageous the after barbette was lower and the gun shorter than in Furious, so that tubes placed outside the sweep of the gun shield (turret) were subject to much greater blast. Meanwhile two triple tubes on each side (plus two single above-water tubes) were approved for Furious largely because of her special role as a carrier and her limited gun armament (later they were given up because they crowded her topsides too badly).
The Vice Admiral commanding the Grand Fleet light cruisers from Courageous wanted torpedo tubes, but he also knew how much work would be involved.31 C-in-C (Beatty) was ‘extremely averse to losing the services of the Glorious until the moment is propitious in view of the Light Cruiser situation and the strength of the enemy in this area. . . the end of the year would be suitable’. Material might not be available before then. The project survived because torpedo tubes were considered so important on board a ship leading the light cruisers.
The simplest scheme, to fit triple tubes each side of the after turret, was objectionable only due to the blast of ‘Y’ turret. In November 1917 a single tube was ordered fitted to the upper deck each side abreast of ‘Y’ turret of HMS Glorious for blast trials, which apparently proved successful.32 Plans called for four sets of fixed triple tubes on the upper deck aft and another two on each side in the Marine mess or in other mess places. The twelve fixed tubes were installed on board Glorious but not Courageous, in twins before and abaft ‘Y’ barbette, with another two tubes side by side at the foot of the mainmast, let into the ship’s side. Courageous but not Glorious was fitted with extensive mine rails on her quarterdeck (which she apparently never used). Presumably this installation made torpedo-tube installation less attractive.
In 1918 the British reviewed overall torpedo policy. They decided that 25 knots was too slow for torpedoes fired at targets which might be making 30 knots. For the future, minimum torpedo speed should be 29 knots – with a range of 18,000 yds. A new 21in Mk V was conceived specifically as a browning-shot weapon to be used from above-water tubes, with a range of 15,000 yds at 29 knots. It was intended for capital ships with above-water tubes (Hood, Furious, Glorious class and Renown class), for the carrier Eagle, for the Raleigh class cruisers, to ‘D’ and ‘E’ class cruisers and for flotilla leaders and ‘W’ class destroyers. The Mk VI was a new torpedo intended to provide the desired 18,000 yds at 29 knots. To do that, it had to be 4ft longer than the Mk IV, hence could not fit existing tubes. Whether destroyers should have the much longer tubes needed for very long range torpedoes became a major post-war design issue. Two were tested in 1919 at the Loch Long range and also from a special tube on board HMS Acasta. Mk VI failed its trials and was abandoned. However, there was still interest in exploring the performance of a very long torpedo, so a Mk IV was lengthened.
The initial approach was to lengthen torpedoes to increase air-flask capacity, but the torpedo designers recognised that a fatter torpedo would be more efficient. In 1918 approval was given to produce three experimental torpedoes of the same length (27ft 3in) but of about 26in diameter. The torpedo would have three settings: long range (20,000 yds at 30 knots), medium speed and high speed. The charge would be increased to 750lb. The 1919 Vernon Annual Report listed characteristics for alternative 25in and 26in designs with length (weight) of 324in (5717lb) and 336in (6251.6lb). In 1920 a Mk IV* was covered in a wooden shell to simulate a 26in torpedo.
A 24.5in calibre was chosen; estimated weight was 5340lb and length 26ft 4½in. Proposed innovations included a turbine engine and a tubular air vessel (air and oil in tandem bottles, with water in the space around them). This torpedo was adopted for the projected post-war capital ships; it armed the two Nelsons. The quest for range continued with the adoption of oxygen-enriched air (which the British called ‘enriched air’). Nominal range of the Nelson class torpedoes was 20,000 yds at 30 knots (15,000 yds at 35 knots). Plants to produce ‘enriched air’ were installed on board the Nelsons and the initial ‘County’ class cruisers. In deck installations such torpedoes caused some problems, particularly during lightning storms, but there were no problems on board the Nelsons. These weapons were not retro-fitted to any earlier ships.33
In 1921 First Sea Lord (Beatty) and C-in-C Atlantic Fleet pointed out that torpedoes offered the battle fleet a massive unseen means of attack. Their threat might force the enemy’s tactical choices. By constantly changing course to avoid torpedoes an enemy would accept a gunnery disadvantage (most fire-control systems demanded that the firing ship maintain a steady course). On the other hand, the rear of the battle fleet would seldom be able to use its torpedoes, the enemy battle fleet still had to contend with the mass of torpedoes aboard British light forces and eliminating battleship torpedoes would save considerable weight and cost. With two fleets running on parallel courses, the existing 16,000 yd 21in torpedo (running time 15 minutes) could not be fired outside 14,000 yds. The 24.5in torpedo in the Nelsons offered greater range (20,000 yds) but also greater running time (5 minutes). Tactical experiments conducted with the Blue side at a torpedo advantage led C-in-C Mediterranean to comment in 1927 that ‘the extent of the Battle Fleet torpedo menace to the Red side can be overestimated’. At this time policy was to avoid night fleet action and opportunities for a surprise encounter declined as screening efficiency improved. British tactical policy was to close the range to achieve decisive results. The fleet might have to go into enemy torpedo water. It would gain an advantage if the enemy fleet were known not to have any torpedoes. If the enemy knew the British had no torpedoes he might be more willing to fight at the shorter ranges the British sought. However, capital ship torpedoes retained some value and obviously more for the inferior fleet. If the Washington agreement were abrogated, the British might find themselves in the inferior position. Tubes were retained.
As bulged and otherwise modernised in the 1920s, battleships retained their four underwater tubes. However, in December 1929 Controller (Admiral Backhouse) proposed that the after torpedo tubes be removed in order to improve watertight subdivision and survivability.34 Backhouse considered the Royal Navy behind others in watertight subdivision. Pre-war ships had inherently poor protection against underwater attack; every opportunity should be taken to improve it. Warspite had just suffered flooding through a torpedo tube. Not only the large torpedo flat but also a large hold compartment below might flood. The impetus for the change seems to have been the US Navy’s decision to remove submerged tubes from its ships upon reconstruction (ACNS’ rebuttal was that ‘they have even less experience of modern battleship action than we have’). DTM agreed that any substantial improvement in underwater protection was more valuable than half their torpedo batteries. The tubes were ordered removed as ships came in for large repairs. That applied to Valiant, which was currently