Unable to dive

I was heavily depth charged in my last patrol which resulted in the destruction of my bow dive planes. I was sinking badly so I blew ballast. Anyway, I still had fish in my tubes but whenever I tried to dive, it would only go to 8m depth and stay there. My patrol area was very far so rather than get attacked by a destroyer or something, I just exited my patrol.

Is there any other way to dive or is it impossible without the bow dive planes?