Guns
Limits on total tonnage were one thing, but without limits on armament or rate of new construction, a new generation of capital ships could still be built. If these were dramatically more powerful than existing vessels, it could still trigger a building race.
The issue of armament was regarded as the most pressing. In July, the British had proposed a ‘standstill’ in naval gun types, with no new guns to be introduced into service for the next ten years. Naturally, this met with objections from almost everyone, once they realised it would allow only the British to build battleships with 18” guns.
Even if the Americans were allowed to introduce their powerful 16” Mk.2, which had already been developed for the ‘South Dakota’ class, the Japanese would be stuck with a less capable 16” gun, the Dutch and Italians with 15”, and the French with 13.4”.
However, the British knew their 18” Mk.1 was a less than optimal design, and that any further ships would be built with a new 45-calibre version of the gun, which would probably have even more severe blast effects. Their delegation did not take much convincing to agree a limit of 16”, and in so doing formally announced that Rodney was armed with this calibre. This came as a pleasant surprise to the Americans, who had suspected that she was armed with 18” guns.
This revelation made a limitation on gun calibre far more realistic. If Rodney had been equipped with 18” guns, the Royal Navy would have possessed the only two 18” ships in a world otherwise limited to 16”. This still left the lone battlecruiser Furious, but with only six guns and a declared displacement of 36,000 tons, American designers had concluded she was not a disproportionate threat on her own.
Based on their knowledge of British construction techniques and the design of the later HMS Hood, the Bureau of Construction and Repair had concluded that Furious probably had a 9” belt, with a thin upper belt and an lower armoured deck no more than 2” thick. Her top speed was clearly at least 32 knots and based on the known specifications of the British 15” gun, she probably had a broadside of about 19,000lbs. It was therefore unlikely that she was significantly superior to their own designs for Lexington, a 33-knot ship with a 9” belt and a broadside of 17,600lbs.
The Japanese had come to the same conclusion, and regarded their ten-gun Amagi design as superior to both the American and British battlecruisers.
A limit of 16” was therefore practical, and the British returned to their ‘standstill’ proposal, modified so that the three smaller powers would be permitted to develop a new gun of up to 16” calibre. In addition, both Japan and the USA had 16” guns in development with a length of 50-calibres, and the American ‘South Dakotas’ were designed to mount this 16” Mk.2. However, the versions currently in service in Britain, Japan and the USA were 45-calibres long, and an agreement was reached to restrict any future designs to using these shorter guns.
This was later amended to permit the deployment of the American 16” Mk.2 aboard two vessels, while the Japanese received favourable terms regarding their ability to complete new ships.
All three major parties subsequently agreed not to develop any new guns with a calibre of more than 8”, while the three smaller nations would be allowed to develop a gun of up to 16” calibre. The Royal Navy would be allowed to keep the eight guns that were available for Furious (six on the ship and two spares), but no more 18” guns would be permitted.