[sublynx]

This is a U-boat's crash dive procedure:

1. An electric bell gives the alarm.
2. The bridge watch prepares the bridge (close voice tube, demount portable machine guns, remove water-tight binoculars from UZO, remove radar detector aerial if necessary, etc.).
3. Simultaneously, vent valves for ballast tanks 5, 2/4, Quick diving tank (if empty) and 3 are opened in that order flooding from bow to stern to overcome the natural stern heaviness of the boat. If fuel is in ballast tanks 2 and 4, the main vent valve is opened with the inner vent valve remaining closed to equalize pressure in the ducts.
4. Simultaneously, the Petty Officer of the Watch goes below to his action station at the forward hydroplanes; the port quarter look-out follows to his action station in the conning tower with the Commanding Officer. The starboard quarter look-out goes below to the after hydroplanes. The Officer of the Watch is the last to go below. It is his duty to close the conning tower hatch. He then goes to his action station in the Control Room.
5. Simultaneously, close Supply and Exhaust air ventilation valves and any other openings in the pressure hull.
6. Planesmen position fore plane down and stern plane up. If it is a crash dive personnel not on watch might be ordered to move to the forward torpedo room to help get the bow under water. Initial angle of dive 4-7° to avoid propellers "racing".
7. Simultaneously, engine room personnel shut down and unclutch Diesel engines and shut the external air intake and exhaust valves.
8. Simultaneously, electric motor room personnel start electric motors
9. When the desired down angle is achieved (normally 12-15° but can go as high as 30 ° in a crash dive - at more than 40° acid may leak from battery cells) vent valve for ballast tank 1 is opened.
10. Simultaneously, the planes are brought to neutral position. Shut off Papenburg depth gauge at 18 meters and Precision depth gauge passing 20 meters.
11. Quick diving tank is blown just short of empty to avoid releasing bubbles. This should result in the boat being at slightly positive buoyancy because the Regulating/Compensating tank is adjusted and maintained to achieve that.
12. Once tanks are flooded, the valves are shut
13. When desired depth is approached forward dive planes were moved up and stern down to level the boat at desired depth.
14. Boat is maintained at depth dynamically by use of the dive planes.
15. Because air in the regulating tanks compressed with increasing depth the boat would grow heavier and the ballast pump or compressed air would be used to keep the boat at slightly positive buoyancy the opposite would occur if the boat moved to a shallower depth and water would be taken in.

There' a lot can go wrong in a procedure this complicated. The seamen in a U-boat are also tired and stressed, their close ones might have just died in the Eastern Front or in the bombings of German cities and most of the seamen are recruits, not professional soldiers with years of practice behind them.

However I agree with CaliEs that the failure percentage could be smaller. Playing the game might get too difficult with the values now planned. I hope that the values can be changed easily to match each player's preferred difficulty level.