Great Britain
The basic design for the G3-class battlecruiser was accepted by the Admiralty Board in February 1921, and the final version was approved that August. Orders were drawn up and placed in late October. Names for the four battlecruisers had never been decided by the Admiralty, and they were simply referred to as No. 1 to No. 4. However, by the end of 1921, two options were up for consideration. One was based on the patron saints of the countries that made up the United Kingdom, St Andrew for Scotland, St David for Wales, St George for England and St Patrick for Ireland, or more accurately Northern Ireland, following the partition of Ireland that May.

The other option, and probably the leading contender, was the reuse of the names of earlier battlecruisers. These were Invincible, Inflexible, Indomitable and Indefatigable. Two of these names, Invincible and Indefatigable had last been given to battlecruisers which had been sunk at Jutland five years before. The remaining two, Inflexible and Indomitable, belonged to existing 12in-gun battlecruisers, which had been decommissioned the previous year, and were then lying in reserve at the Nore. Both were eventually sold for scrap and were broken up in 1922. This meant these names were free to be used for the new G3 battlecruisers, if they were built.

The shipyards allocated for the new battlecruisers’ construction were William Beardmore & Co., John Brown & Co. and Fairfield Shipbuilding & Engineering Co. on Clydeside and Swan Hunter on Tyneside. The latter, though, was unable to produce all of the propulsion system themselves, and so the work was subcontracted to C.A. Parsons & Co., also on Tyneside, who were world leaders in the production of marine steam turbines and boilers. The laying down of these ships was delayed for two reasons. First the government was awaiting the outcome of the Washington Conference, which might well lead to the cancellation of these ships. Just as importantly, the Admiralty still had to secure funding for their construction. In the end, the orders were cancelled on 13 February 1922, before any of the four battlecruisers had even been laid down.
The second part of the Admiralty’s plan to modernize the post-war fleet was the building of the four N3-class battleships. If funding for the project was found, these were due to be laid down in 1922, but planning for them was not as well advanced as the battlecruisers. So, in February 1922, before the final designs had been completed, and set before the Admiralty Board for approval, the decision was made to cancel these ships’ construction. Even if the Washington Naval Treaty hadn’t led to the cancellation of this project, in the aftermath of the war Britain was so cash-strapped that it was extremely unlikely that the British treasury would have approved the funding of this project. They remain, though, in their half-finished form, a glimpse of what might have been – Britain’s possession of four of the most powerfully armed battleships in the world, and the largest ever built for the Royal Navy.

Imperial Japan
The Japanese drive to build a small but balanced fleet placed a heavy burden on the country’s finances. However, the country still managed to produce a steady trickle of well-designed battleships and battlecruisers, which pushed the naval architects in other countries to improve their own designs. The Kongō-class battlecruiser, for example, was better protected than many of its foreign counterparts, while the Fuso-class battleships were faster than dreadnoughts in American or British service. The Kaga-class battleships were improvements of the earlier Nagato design, with a greatly improved layout of armour – the result of an analysis of Jutland. These would have been powerful additions to the Imperial Navy, but the two battleships of the class had the misfortune of being launched in late 1921, just as the Washington Naval Conference was under way. As a result, work on them was halted on 5 February 1922.

They remained on the stocks, and in April 1924 Tosa was cancelled, and her guns handed over to the army for use in coastal defence batteries. The hulk was then used as a gunnery target and sunk in February 1925. Kaga though, was spared a similar fate thanks to the Tokyo earthquake of September 1923. The battlecruiser Amagi, which had been earmarked for conversion into an aircraft carrier, was damaged beyond repair. So, Kaga was converted in her stead, and was completed in 1928. The other battleship victims of the conference were the four ships of the Kii class, which were a merger of the battleship and battlecruiser.

Kii was to be built in the Kure Naval Yard and Owari in the naval yard at Yokosuka. The remaining two of the class hadn’t received names, and so were known as No. 11 and No. 12. They were earmarked to be built by Kawasaki in Kobe and Mitsubishi in Nagasaki respectively, after the two Kaga-class battleships had been launched. Kii and Owari were ordered in October 1921, but had not even been laid down before their construction was halted. Their two unnamed sister ships hadn’t even been ordered when they were cancelled in November 1923. Kii and Owari too were eventually cancelled in April 1924.

The Amagi class of four battlecruisers were essentially enlarged versions of the Kaga-class battleships, but with less armour and greater speed. They were laid down in two batches, in late 1920 and then late 1921. With completion expected to take three years, they were all still on the stocks when the Washington Naval Conference began. All work on them stopped on 5 February 1922, and while two were to be scrapped, the terms of the treaty allowed two more to be converted into aircraft carriers. Inevitably, as they were the most complete, Amagi and Akagi were chosen for conversion.

The other two were cancelled that summer and broken up in situ two years later. Work on Amagi and Akagi was scheduled to begin in late 1923, but that September the Tokyo earthquake struck Yokosuka, and Amagi was damaged beyond repair. So, she was cancelled, and was subsequently scrapped on the slipway in April 1924. In her place, the battleship Kaga underwent conversion instead. In Kure, work on the conversion of Akagi began in November 1923, and was eventually completed in 1927.

The final batch of Japanese capital ship projects to be cancelled in the wake of the treaty were the No. 13-class battlecruisers/fast battleships. These ships were never given names, but instead were simply referred to by their number. No. 13 was to be built in Yokosuka Naval Yard, No. 14 in Kure Naval Yard, No. 15 in the Mitsubishi shipyard in Nagasaki and No. 16 in the Kawasaki yard in Kobe. They were all due to be ordered in February 1922 and laid down that summer. All four ships were due for completion in 1927. Instead, all orders were cancelled on 5 February 1922, before work on them had even begun. With their planned armament of eight 18in guns, a speed of 30 knots and an armoured belt 13in (33cm) thick, if built, these would have been among the most powerful warships in the world.