eliminated protruding components that created drag with earlier models. The new, streamlined hull design allowed submerged speed of , versus for the Type VIIC. The ability to outrun many surface ships while submerged, combined with improved dive times (also a product of the new hull form), made the Type XXI much more difficult to pursue and destroy. It also provided a 'sprint ability' when positioning itself for an attack. Older boats had to surface to sprint into position. This often revealed a boat's location, especially after aircraft became available for convoy escort. The Type XXI was also equipped with an additional pair of electric creep motors for occasions when silent running was necessary. The Type XXI was equipped with six bow torpedo tubes (instead of the more common four in German submarines) and carried 23 torpedoes. It featured an electric torpedo-reloading system that allowed all six bow torpedo tubes to be reloaded faster than a Type VIIC could reload one tube. The Type XXI could fire 18 torpedoes in less than 20 minutes. The class also featured a very sensitive passive sonar for the time, housed in the "chin" of the hull. The Type XXIs also had better facilities than previous U-boat classes, with much roomier crew berths, and a freezer to prevent food spoilage. The increased capacity allowed for a crew of 57. A post-war assessment of the Type XXI by the United States Navy concluded that while the design had some admirable features, it was seriously flawed. The submarines' engines were underpowered, which limited the surface speed and increased the time required to charge the batteries. The hydraulic system was unduly complex, and its main elements were located outside the pressure hull. This made the system highly vulnerable to corrosion and damage. The snorkel was also badly designed, and difficult to use in practice. Construction This was the first U-boat to be constructed of modular components to allow for the manufacture of the various components in different factories and subsequent assembly at the shipyard. Between 1943 and 1945, 118 boats were assembled by Blohm & Voss of Hamburg, AG Weser of Bremen and Schichau-Werke of Danzig. Each hull was constructed from nine prefabricated sections with final assembly at the shipyards. This new method allowed for a hypothetical construction time of less than six months per vessel, but in practice all the assembled U-boats were plagued with severe quality