Submarine age is more than a calendar problem because every diving cycle stresses the pressure hull and can reduce the depth at which crews should trust it. O 9 and O 10 nevertheless escaped to Britain, patrolled the Channel and Bay of Biscay, and later supported anti-submarine training. O 11 had already been rammed, raised, and put under repair before the German invasion forced the Dutch to scuttle her. Germany raised the roughly twenty-year-old boat and continued spending resources on repairs into 1944 without returning her to useful service. Her story connects material fatigue to the strategic cost of pursuing a captured asset past the point of practical value.
Notable Point · 1:49:40-1:55:28
O 9 class: aging pressure hulls and Germany's costly salvage effort
The elderly O 9 class illustrates how diving cycles consume pressure-hull life and how Germany spent years trying to recover a marginal captured boat.