Post-captain

An exception to this rule was that a very junior post-captain could be posted to command an admiral's flagship, which was almost always a large ship of the line.

The admiral would usually do this to keep his most junior captain under close observation and subject to his direct supervision.

After 1795, when they were first introduced on Royal Navy uniforms, the number and position of epaulettes distinguished between commanders and post-captains of various seniorities.

A post-captain with less than three years' seniority wore a single epaulette on the right shoulder and a post-captain with three or more years seniority wore an epaulette on each shoulder.

In the O'Brian series, Aubrey "wets the swab" – that is, he celebrates his promotion to commander and the acquisition of his "swab" or epaulette with the consumption of copious amounts of alcohol.