Reaching lieutenant was relatively routine, but each later step demanded stronger evidence of specialist skill and command potential. Commander and captain were major exit points because the service needed far fewer officers at each higher level. Competent officers could therefore leave at those ranks without having failed professionally. The narrowing promotion pyramid explains why wartime retirement lists contain many capable officers.
Chapter · 8:48-10:29
Why the Royal Navy promotion pyramid narrows
The opening argument traces how officer selection becomes progressively tighter from lieutenant through commander, captain, and flag rank.