In-between World Wars
World War I ended signing the Treaty of Versailles, and so deadly had the U-boats been that Germany was specifically banned from having them. That might have been the end of military submarine except that the seeds for World War II were contained in the Treaty of Versailles, and the military submarine would continue to develop.
The victors of World War I split up the remaining U-boats for examination and testing. During the period between the World Wars, submarine development continued at a steady pace.
United States and Britain efforts were concentrated on the creation of long-range `fleet` submarines designed to support the battle fleets. They designed and constructed some experimental models with heavy guns (as much as 12 inches) and tried to use submarines as aircraft carriers, though never with much success.
Germany. The Treaty of Versailles blocked the German Navy from having submarines and limited the number of officers to 1,500. One of those officers was U-boat skipper Karl Dönitz. He began developing submarine tactics for the next war.
In secret, Germany acquired a Dutch shipbuilding company that designed submarines ostensibly for sale to international customers but that also were prototypes for the next class of German U-boats. In fact, it would be German crews that conducted sea trials in 1931 for three boats sold to the Finnish Navy.
In 1932 the German government approved the clandestine construction of 16 new U-boats. On March 16, 1935 German Chancellor Adolf Hitler renounced the Treaty of Versailles. A few weeks later, the first of a new series of U-boat, U-1, entered service.
As in World War I, Germany developed several classes of U-boat. Typical were the coastal boats (Type II), long-range boats (Type IX), and jack-of-all-trades boats (Type VII), which became the mainstay of the fleet, with more than 700 completed in six variations (A through F) by the end of the war. Typical displacement at the surface: about 760 tons. Length: 220 feet. Range: 8,700 miles, with a functional endurance of seven or eight weeks without refueling. Dive time: Twenty seconds, with a maximum safe depth of 650 feet.
Japan, as one of the World War I allies, Japan received seven of the surrendered U-boats but went a bit beyond mere `examination.` Japan imported some 800 German technicians, engineers, and naval officers to teach them how to design and build submarines.
Japanese submarine designers moved out from under the shadow of the Germans and, on their own, focused on three basic classes: the I-boats, most of them about the size of the German U-cruisers; the RO coastal boats, roughly the size of the German Type VII but not as capable; and the HA series of midget submarines, in many variations.
The Japanese were more serious about submarine aircraft carriers than any other navy: They built their first, the 2243-ton, 320-foot I-5, in 1932. It was equipped with one floatplane. In the next 12 years, they built 28 more, in ever-increasing sizes.
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