At the time of IvS, the Germans were bound by the Treaty of Versailles, signed in 1919. This treaty, among other terms, demanded that all German U-boats be destroyed or given to other nations. Thus the Reichsmarine was left without a submarine capability, and IvS was created to work around these restrictions. The work of the company was a major factor in the foundation of the Kriegsmarine of World War II.
Submarine sales
IvS first designed two submarines based on the World War I UB III of the Kaiserliche Marine. Both were built in the Feijenoord district of Rotterdam in 1927 and sold to Turkey, which named them TCG Birinci İnönü and İkinci İnönü. They were followed by the Submarino E-1 built in 1930 by the Echevarrieta y Larrinaga shipyard in Cádiz, Spain, initially for the Spanish Navy, but mainly as a prototype of the German Type I submarine. However, the Spanish lost interest in the E-1, and it was also sold to Turkey in 1935 as the TCG Gür. The E-1 also attracted the attention of the Soviet Navy; with significant modifications the E-1 became the E-2 project. Construction of the first two prototypes started in December 1934 at the Baltic Shipyard in Leningrad, using German diesel engines and electric batteries. They were followed by the third prototype in April 1935. With further modifications to use less-expensive Soviet equipment, full production began in 1936 of the Soviet S-class submarines. From 1927 to 1933 four IvS-designed submarines were built by Crichton-Vulcan Oy in Turku, Finland. One of these, CV 707, was the prototype of the German Type II submarine, while three larger Vetehinen-class submarines served as the prototypes for the Type VII. A fifth IvS design was the small submarine Saukko, built in Helsinki by the Sandvikens Skeppsdocka och Mekaniska Verkstad shipyard, and originally planned to be deployed in Lake Ladoga. The contracts were worded in such a way that IvS employees were involved with crew training and selection, and were also allowed to take part in submarine service trials. The Germans - who were, at the time, tightly restricted from using submarines themselves - thus gained first-hand knowledge of how their prototypes worked in practice.
Later projects
In 1933, the Reichsmarine established a training school in Kiel for U-boat crews, called the Unterseebootsabwehrschule. This program provided for a small fleet of eight 500-tonne submarines, later doubled to sixteeen. Later plans for an actual U-boat fleet included designs for submarines referred to as "Experimental Motor Boats". Deutsche Werke in Kiel was selected to build the new submarines, and a new U-boat base was to be built at Kiel-Dietrichsdorf. Submarine components were gathered there surreptitiously, in preparation for the order to begin production. The following submarine types were initially planned:
1934 - two large and two small U-boats.
1935 - four small U-boats.
1936 - two large and six small U-boats.
1937 - two large and six small U-boats.
From then on more boats were built, leading up to wartime production.
The company also designed the Finnish Navycoastal defense shipsVäinämöinen and Ilmarinen in the late 1920s. Both ships were also built by Crichton-Vulcan Oy, entering service in 1932 and 1934, respectively.
Battlecruisers
The IvS was also involved in designing plans for a Royal Netherlands Navy project to build battlecruisers. Battlecruisers were deemed by some to be essential for the defense of the Dutch East Indies against possible Japanese expansion, especially as the Netherlands lacked any large surface ships. The designs were heavily influenced by the German and the final design was similar to the IvS design, because the Germans were expected to at least furnish the gun turrets for these ships, as constructing them was beyond Dutch capabilities. In the end, political disagreements delayed the decision-making process and none of the projected ships were laid down, as on May 10, 1940 the Germans invaded the Netherlands.
