They also were not (usually) designed for deep diving. They could not use the 3rd dimension very well.
They dived about as deep as British and US subs of the era.
Most British subs from the late 1920s had a test depth of 300ft. The U class was 200ft but increased in later ships to 300ft but they were designed for use in shallower waters anyway. The T class saw it increased to 350ft by using thicker plate for the pressure hull and more welding in later wartime boats. The RN went to 500ft with the A class designed in 1942/43, which was just entering service as the war ended.
Pre-war the USN went from 200ft with the S class of 1918 to 250ft for most of its inter-war classes. The Gato class (completed from Dec 1941) was 300ft, increased to 400ft in the succeeding Balao class (from Feb 1943) and Tench classes. That increase was achieved by using thicker pressure hull plates and high strength steels. It was later increased to 450ft when more powerful pumps able to operate at increased depths became available late in WW2.
Japanese submarines inter-war went from 200ft for most of the 1920s to 250ft in the early 1930s to 330ft in the late 1930s and wartime boats.
The above are the test or operational diving depths. Usually submarines, at least those for the RN, were tested on trials to about 10% greater. Crush depth was usually taken to be about double the test depth. But at the time but the mathematical formulae required to accurately predict failure depthsand the various stresses, had to await computers in the post WW2 era. Subsequently a lot of the ideas about the stresses on a sub pressure hull shape of this era proved to be inaccurate.
It was the Germans who attained significantly greater diving depths. At the start of WW2 Type VII & IX were good down to 220-230m (722-755ft) with later Type VII boats able to go to 250m (820ft) or even 270m (886ft). Britain got a close look at the construction of a Type VII when U-570 was captured in Aug 1941. Sir Stanley Goodall, the DNC at the time, could not see why she had so thick a pressure hull and such flimsy frames. That started a reassessment of just how a submarine pressure hull should be designed. What is not clear to me is whether the Germans had a better understanding or simply arrived at it by chance. It also forced a reassessment of the necessary settings on depth charges to ensure that they could explode that deep.