Carrying on from Post 129...
At the end of 1929 the British Commonwealth had 59 cruisers (including 4 under construction) with a total standard displacement of 368,530 tons as follows:
The displacements come from Lenton and Colledge. I don't have standard displacements for the Weymouth to Centaur classes. Therefore I have had to use the standard displacements for Adelaide and the Caledon classes as applicable.
However, the requirement was for 70 cruisers, so the British Commonwealth was 11 ships short.
The newly signed London Naval Treaty allowed the British Commonwealth to have 339,000 tons of cruisers made up of 146,800 tons of ships armed with 8" guns and the 192,200 ton of ships armed with 6" guns.
The 4 Hawkins class cruisers would have had to be discarded by the end of 1936 or rearmed with 6" guns to comply with the Treaty. However, Vindictive and Hawkins would be over age by the end of 1936 anyway and the Treaty allowed for the disposal of Effingham and Frobisher in 1936.
Under the terms of the treaty 37 ships with an aggregate displacement of 184,940 tons would become overage by 31st December 1936. However, the Treaty also said,
Apart from the cruisers under construction on 1 April 1930, the total replacement tonnage of cruisers to be completed, in the case of the British Commonwealth of Nations, prior to 31 December 1936, shall not exceed 91,000 tons (92,456 metric tons).
The 91,000 tons of cruisers that the British Commonwealth was allowed to begin after 1st April 1930 and complete before 31st December 1936 was sufficient for 13 Leander class ships.
As far as I can work out the projected cruiser force for 31st December 1936 in 1929-30 was as follows.
The Royal Navy still required a minimum of 70 cruisers so the force it was allowed was 21 short of the number that it wanted.
Of the 21 Birmingham to E class ships:
- 14 ships of 62,860 tons would be overage on 31st December 1936 and;
- 5 ships of 23,940 tons would become overage by 31st December 1938 and;
- 2 ships of 15,130 tons would become overage in 1942.
However, as usual things didn't go according to plan.
- Only 16 of the 23 cruisers that should have been scrapped by the end of 1936 were disposed of. The 7 ships that survived were the 3 Caledon and 4 Hawkins class cruisers;
- The 91,000 tons was used to order 5 Leanders, 3 Amphions, 3 Arethusas and 2 Southamptons, which is still a total of 13 ships. They were ordered in the 1929-30 to 1933-34 Navy Estimates and used 90,500 of the 91,000 tons available.
The First London Naval Treaty allowed replacements for cruisers that would become overage in 1937, 1938 and 1939 to be laid down before 1st January 1937. This was used to order 9 cruisers were ordered in the Navy Estimates for the 3 financial years 1934-35 to 1936-37. They were the fourth Arethusa, the 6 remaining Southampton and the 2 Edinburgh class cruisers.
The 22 ships of the Leander to Edinburgh classes ordered from 1929-30 to 1936-37 had a total displacement of 171,270 tons. Therefore, 20,930 ton remained from the 192,200 tons of 6" cruisers allowed by the Treaty. However, 15,130 tons of this was absorbed by the 2 E class cruisers. They would not become over age until 1942 and under the terms of the Treaty their replacements could not be laid down until 1939. Therefore, only 5,800 tons of cruisers could be begun 1937-38, which was only enough for one Arethusa class cruiser.
There would also be a gap in cruiser construction between laying down the E class replacements in 1939 and 1942 because the first County class cruisers would not become over age until 1945.
Fortunately, the tonnage quotas were abolished by the Second London Naval Treaty. Otherwise it would have been impossible to build the 11 Colony and 10 Dido class cruisers ordered in the 1936-37 to 1939-40 Navy Estimates. My guess is that instead of 21 ships ordered IOTL the 20,930 tons that were available would have been used to build 3 Amphions or 2 Edinburghs, which would have been laid down in 1939 for completion in 1942.