Under the 1940 and 1941 War Programmes, a further 41 U boats were ordered, but only 34 were completed. This second group of U Class submarines did not differ substantially from the first, but an approximate increase of 5 feet in the stern gave them a more streamlined shape aft and improved the flow of water over the propellers.
In addition to their four 21-inch stern tubes and three 0.303-inch portable machine-guns, the U boats were fitted with a 3-inch gun forward of the conning tower. However, as this was an afterthought to the original design, no separate hatch was fitted for the gun crew or ammunition. This resulted in the conning tower becoming extremely crowded before and after gun action and, if the gun crew was employed, rapid crash-diving was impossible.
