The U class put underwater performance first

The U class marked a decisive shift away from treating the surface run as the main part of a submarine's work. The boats were intended to leave Gibraltar, Malta, Alexandria, or a North Sea base, spend as much time underwater as possible, ambush targets, and return. Their short range was an acceptable trade because the intended patrol areas lay close to those bases. Extensive trials emphasized streamlining, quiet approach, and underwater performance. Those lessons fed back into later versions of the larger S and T classes and influenced submarine development beyond Britain.