Heavy Cruiser - 1930s: London Treaty

1930s: London Treaty

In 1930 the Washington Naval Treaty was extended by the London Naval Treaty, which finally settled the arguments on cruisers which had raged in the 1920s. The treaty defined limits on both heavy cruisers - those with guns larger than 155 mm (6.1 inches) - and light cruisers - those with smaller-calibre guns. The limit of 10,000 tons displacement still applied to both. This was the point at which the split between 'heavy' and 'light' cruisers finally became official and widespread.

The Treaty satisfied Britain and America. However, it deeply offended Japan, as this severely limited the numbers of heavy cruisers that the Imperial Japanese Navy could have, as they considered heavy cruisers as key warships in a line of battle with their 8-inch guns and heavy torpedo armament. The IJN placed less priority on purpose-built light cruisers, most of their existing types dating back to the 1920s (the five WWII-era light cruisers that the IJN commissioned were less well-armed than light cruisers of the US and Royal Navies), which were largely relegated to leading destroyer squadrons. The solution the Japanese adopted was to build the Mogami class, which was declared as a 10,000 ton light cruiser with fifteen 6.1-inch guns. In practice, they displaced over 12,000 tons, and it was always intended to replace her turrets to give a final armament of ten 203 mm guns, making something of a nonsense of the light and heavy cruiser classifications.

The German navy also paid lip-service to the treaty limitations, with the Admiral Hipper class weighing in at 14,000 tons.

In the mid 1930s, Britain, France and Italy ceased building heavy cruisers. It was feltthat in a likely cruiser engagement, a larger number of 155 mm (6-inch) guns would be preferable to a smaller number of 203 mm (8-inch). The heavier shell of the 203 mm weapon was of little advantage, as most ships that could withstand a 6-inch hit were also well-protected against 8-inch shells. This led to the construction of cruisers up to the 10,000-tons limit, with twelve to fifteen 155 mm guns. While these ships fell into the 'light cruiser' classification by virtue of the calibre of their main armament, they were designed to fight a heavy cruiser on equal terms again making something of a nonsense of the classifications..

The 1936 London Naval Treaty, principally negotiated between Britain and the United States but never ratified, abolished the heavy cruiser entirely by restricting new construction to 8,000 tons and 155 mm (6.1-inch) guns. This suited Britain's needs very well, but was largely a dead letter. The U.S. continued to build heavy cruisers, culminating in the New Orleans class and USS Wichita.