from 1794 the admiralty allowed a crew of 121 for a 16-gun sloop such as hms "calypso". the commander and lieutenants were professional sea officers, trained in gunnery, navigation and seamanship in equal measure and appointed to the ship by admiralty commission. the lieutenants were all at least nineteen years of age, having served a minimum six-year apprenticeship as midshipman or master's mate before undertaking and passing the examination for lieutenant. the commander would usually have been an experienced lieutenant who had come to the attention of the admiralty or his commander-in-chief through some distinction in service or by having an influential patron. the commander's duties were almost identical to those of a post captain, although on a smaller scale, the exception being that as a commander he had no automatic rights of promotion to the flag list and could quite easily remain a commander for the rest of his career.