the ship's roll as the "second captain" and "first captain", respectively. 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 commander wore a single epaulette on the left shoulder. 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. The term post-captain was descriptive only; no one was ever styled "Post-Captain John Smith". See also Rating system of the Royal Navy Post-ship References External links National Maritime Museum Uniform Collection Royal Navy appointments