Why cautious submarine captains could fail in wartime

Were cautious pre-war US submarine captains replaced because their training discouraged aggressive attacks?

Partly, but expansion and promotion also mattered, and the larger problem was that useful peacetime risk aversion did not always convert into controlled wartime aggression.

A viewer notes that cautious pre-war American submarine captains were replaced by more aggressive officers after combat began. Rapid wartime expansion and promotion also contributed to the turnover. In peacetime, risk-averse commanders protect scarce boats and crews during inherently dangerous training. War requires a different balance: calculated risk and controlled aggression without reckless waste. Some officers can make that transition and others cannot, which makes selection by peacetime performance an imperfect predictor of combat command.