By mid 1943, against numerous, well-trained and effectively used escorts, the day of the conventional submarine was drawing to a close. Total numbers stay at around the 400 mark for the remainder of the war. In response to the new Allied technology and tactics the Germans made a series of improvements to their new U-Boats and their weapons, but these come too late to have a major impact on the war. These innovations included:

1. Adding aditional anti-aircraft armament to U-boats. New U-Boats receive multiple 40m and 20mm rapid fire guns.

2. Introducing the "Gnat" acoustic torpedo. This torpedo is designed to respond to the loudest underwater noises- normally the high speed propellors of the escort warships.

3. A Dutch invention, the "schnorkel", allows batteries to be recharged at periscope depth - so that submarines do not need to surface where they are most vulnerable to air attacks. It enters service in mid-1944.