I posted this in another thread. In 1969, the USS Chopper accidently dived to 1,000 feet (about 300 meters).
http://www.geocities.com/jaob/deepdive.htm
It was a WW2 Balao class submarine with a test depth of 400 feet (about 123 meters). WW2 german subs were supposed to be able to dive deeper than US subs, so a VII or IX
should be able to go as deep.
It does not say in the link, but the Chopper's pressure hull was so badly damaged from this extreme depth that the sub had to be taken out of service.