It has been many years since I first saw Das Boot. As usual, the characters and incidents are fictitious, but this is not a Hollywood fiction; the types of events portrayed certainly occurred. While I can’t speak for the makers of the film, it gives a gritty German perspective on the one thing that truly scared Winston Churchill – the U-boat peril.
I relied heavily on Wikipedia to provide accurate information on two U-boat types. Many good sources all have copyright material precluding sharing anything.
I posted this in large part because it seems that the true nature of these boats are still not understood.
In comparison to U.S. subs, U-boats were considerably smaller. A plethora of types were planned, some boats were short ranged and used close to British waters; others, far fewer in numbers could operate off the U.S. coast, and the rest operated in the mid Atlantic. One design improvement (such as a single aft torpedo tube) only increased their torpedo capacity to 14 total.
U-Boat type VIIC depth limits: The theoretical crush depth of the Type VIIC was 280 – 375 meters, depending on which figures are used. Design depths from 120 to 150 meters are published. The Germans generally used a safety factor of 2.5 to get design depth and they tested the hull at a safety factor of 1.5.
The maximum safe depth for the VIIC was therefore between 185 and 250 meters. The problem is that most of numbers published do not specify the applicable safety factor, so it is difficult to come up with a precise number for theoretical crush depth. The actual crush depth varied from one boat to another anyway since the quality of the materials and the workmanship varied. SOURCE
Contrast those figures with U.S. Gato class subs depth limits, from WIKI:
The Gato-class were a class of submarines built for the United States Navy and launched in 1941–1943; they were the first mass-production US submarine class of World War II. Together with their near-sisters the andes, their design formed the majority of the United States Navy’s World War II submarine fleet.
The Gato-class design was a near-duplicate of the preceding Tambor and Gar-class boats. The only significant differences were an increase in diving depth from 250 feet (76 m) to 300 feet (91 m), and an extra five feet in length to allow the addition of a watertight bulkhead dividing the one large engine room in two, with two diesel generators in each room. Operational experience with earlier boats led the naval architects and engineers at the Navy’s Bureau of Construction and Repair to believe that they had been unduly conservative in their estimates of hull strength. Without changing the construction or thickness of the pressure hull steel, they decided that the Gato-class boats would be fully capable of routinely operating at 300 feet, a 50-foot (15 m) increase in test depth over the preceding classes.
This will help to understand how deep they might go to escape depth charges:
100 Meters (m) = 328.08399 Feet (ft)
160 Meters (m) = 524.93438 Feet (ft)
220 Meters (m) = 721.78478 Feet (ft)