Jon's questions on the hatches recalls my memories of the procedure for opening same after a long submerging, may be 30 hours or so. On a long time submerged situation everybody except people on watch, the CO and me was in bed using minimum of oxygen. The increased CO2 content in the air made everybody panting heavily. After a strenuous day it happened that an allowance of one cigarette per man was given ( crazy ) but mostly the match would not burn anyhow. When surfacing the CO on the top ladder having a man with a firm grip on his legs, carefully put the catch of the tophatch in position, turned the hatchwheel and the hatch cracked open letting the overpressure out so you felt it heavily on your eardrums. Mostly the foul air in the compartments turned into fog at the quick pressure release before the tophatch was fully open. The overpressure in the sub was due to various air leakages and inboard venting, but mostly by using the airmotor for the outboard group exhaustvalve grinders at the moment of diving.
Tore