Why new U-boats could not replace lost command experience

Dönitz appeared to Hitler to be delivering results, but Allied escort expansion, intelligence work and mass merchant construction were changing the U-boat campaign. Advanced Type XXI submarines would still have required experienced crews able to exploit them. Repeated risk-taking exposed successful aggressive commanders to eventual loss, while caution helped other experienced officers survive. This interpretation describes a tendency, with exceptions: surviving commanders were often either young and aggressive or experienced and conservative. New hulls alone could not replace the combination of experience and judgment lost with veteran crews.