Second London Naval Treaty: Naval Armaments and the Path to World War II
In the volatile years leading up to World War II, global powers attempted to curb the escalating naval arms race through diplomatic agreements. The Second London Naval Treaty was a pivotal effort to limit the growth of naval armaments and prevent a costly, unchecked buildup of warships. While intended to maintain stability, the treaty's effectiveness was hampered by the withdrawal of key nations and the shifting geopolitical landscape of the 1930s.
Key Facts
- Signatories: France, the United States, and the British Empire (including Australia, Canada, India, New Zealand, and the UK).
- Non-Signatories: Japan (withdrew January 15), Italy, South Africa, and the Irish Free State.
- Capital Ship Limits: Initially restricted to 35,000 long tons displacement and 14-inch guns.
- The Escalator Clause: Allowed signatories to increase gun caliber to 16 inches if non-signatories refused to adhere to limits.
- Submarine Protocol: Mandated that submarines follow "cruiser rules," prohibiting the sinking of merchant ships without ensuring crew safety.
- End Date: The treaty effectively ended on September 1, 1939, with the start of World War II.
The Scope and Limitations of the Treaty
The primary goal of the conference was to cap the growth of naval power until 1942. However, the absence of Japan—a dominant naval force in the Pacific—made it impossible to agree on a total ceiling for the number of warships. Instead, the treaty focused on limiting the physical specifications of individual vessels.
The treaty established strict limits on various ship classes to prevent the development of "super-dreadnoughts." Capital ships were limited to a standard displacement of 35,000 long tons and 14-inch (356 mm) guns. To protect against potential aggression from non-signatories, American negotiators pushed for an escalator clause. This provision permitted France, the UK, and the US to increase their gun limit to 16 inches if Japan or Italy remained outside the agreement after April 1, 1937.
Other vessel restrictions included:
- Submarines: Maximum 2,000 tons displacement and guns no larger than 5.1 inches.
- Light Cruisers: Maximum 8,000 tons and guns of 6.1 inches (155 mm) or smaller.
- Aircraft Carriers: Maximum 23,000 tons.
Despite these rules, Article 25 provided a loophole: nations could exceed these limits if another country built ships beyond the treaty's scope and such a move was deemed necessary for national security. By 1938, this led the parties to agree on a new battleship displacement limit of 45,000 tons.
Impact on Battleship Design
The treaty's constraints directly influenced the design of several famous battleship classes. Three primary classes were initiated under these rules: the King George V, North Carolina, and South Dakota.
The United Kingdom chose not to invoke the escalator clause for the King George V class. Redesigning the ships for 15-inch guns would have caused an 18-month delay, and the UK prioritized getting ships into service over maximum firepower. In contrast, the United States invoked the clause for the North Carolina class. Because these ships were designed for easy modification, they were completed with 16-inch guns. However, this created an imbalance, as the armor was not designed to withstand 16-inch fire, leading the US to stop further orders of that class.
The South Dakota class attempted to balance 16-inch guns with the 35,000-ton limit, resulting in a very compact and cramped hull. Finally, the Iowa class, designed in 1938, moved beyond the treaty's limits to a 45,000-ton displacement, featuring improved 16-inch guns and higher speeds, while remaining narrow enough to pass through the Panama Canal.
Naval Specifications Summary
| Vessel Type | Max Displacement | Max Gun Calibre |
|---|---|---|
| Capital Ships (Initial) | 35,000 long tons | 14-inch (up to 16-inch via escalator) |
| Capital Ships (1938) | 45,000 long tons | Not specified |
| Aircraft Carriers | 23,000 tons | N/A |
| Light Cruisers | 8,000 tons | 6.1-inch |
| Submarines | 2,000 tons | 5.1-inch |
The London Submarine Protocol
Beyond ship sizes, the treaty addressed the ethics of underwater warfare. Article 22 of the 1930 Treaty of London established the cruiser rules, which dictated that submarines must operate like surface vessels. Specifically, unarmed merchant ships could not be sunk without first ensuring the safety of the crew and passengers. Lifeboats were generally not considered a "place of safety."
The 1936 treaty reaffirmed these rules, creating the London Submarine Protocol, which was signed by over 35 nations, including Germany and Japan. This protocol later became a central piece of evidence during the Nuremberg Trials of Admiral Karl Dönitz, who was charged with ordering unrestricted submarine warfare.
However, the protocol was practically undermined by the arming of merchant ships. Admiral Dönitz argued that any merchant vessel that was armed or reported submarine sightings became a de facto naval auxiliary, thereby forfeiting the protections of the cruiser rules and making the restrictions moot.
Frequently Asked Questions
Why did Japan and Italy refuse to sign the treaty?
Japan withdrew from the conference on January 15 due to its impending military involvement on the Asian mainland. Italy declined to sign largely because of the international controversy and League of Nations sanctions following its invasion of Abyssinia (Ethiopia).
What was the purpose of the "escalator clause"?
The escalator clause was a safeguard requested by the United States. It allowed signatory nations to increase the maximum gun caliber of their capital ships from 14 inches to 16 inches if non-signatory nations (specifically Japan or Italy) refused to adhere to the treaty limits by April 1, 1937.
How did the treaty affect the design of the South Dakota-class battleships?
To maintain the treaty-mandated 35,000-ton displacement while carrying powerful 16-inch guns and the necessary armor to protect against them, designers had to create a significantly shorter hull, resulting in a very compact and cramped ship.
What were the "cruiser rules" regarding submarines?
The cruiser rules required submarines to treat merchant vessels as surface ships would: they could not sink an unarmed merchant ship without first placing the passengers and crew in a safe location, as lifeboats were not considered sufficient safety measures.
Why did the United Kingdom decline to use the escalator clause for the King George V class?
The UK decided that the 18-month delay required to redesign the ships and develop 15-inch guns was too great a risk. They prioritized the immediate need for new battleships over the advantage of increased firepower.