Short answers, pulled from the story.
The Type VII submarine was a German medium attack U-boat class ordered by the Reichsmarine in 1935. This decision occurred before Adolf Hitler openly renounced the Treaty of Versailles in March that year.
A total of 709 Type VII boats were commissioned across multiple shipyards during World War II. Production began at Deschimag AG Weser in Bremen and Friedrich Krupp Germaniawerft in Kiel, with construction halting abruptly in September 1943 and ending completely by January 1944.
The Type VII program officially began after the Anglo-German Naval Agreement in 1935. At the start of the war on the 3rd of September 1939, only eighteen Type VII boats were in service out of fifty-six commissioned U-boats.
The Type VIIC added a full frame section of 1.5 meters to house sonar equipment which allowed navigation through minefields. This modification reduced speed marginally but enabled operations until 1940 when U-boats operated from French bases where mines were less common.
Between December 1941 and August 1942, Type VII submarines mounted one hundred four patrols off Newfoundland and Labrador. These operations sank two hundred twenty-five ships totaling over one million tons before convoy battles peaked in March 1943.