Why the Royal Navy struggled to rotate exhausted commanders

Why were so many senior Royal Navy officers overworked during the war?

Britain lacked enough trained senior commanders for regular reliefs, while fleet command at sea was a continuous 24-hour responsibility.

The US system alternated or relieved commanders, while the Royal Navy lacked enough senior officers trained for major operational roles. Creating a comparable rotation system before the war might have required roughly doubling the pool of rear admirals and giving them enough experience to take over complex fleets. Cunningham could rotate some subordinates in the Mediterranean, but the Royal Navy often transferred an exhausted officer directly into another necessary appointment. Command at sea remained a 24-hour responsibility because an admiral could be awakened for an operational decision at any moment. Somerville's path from illness through Dunkirk, Force H, and the Indian Ocean is the clearest example of what that personnel shortage cost.