A captain's clerk was a rating, now obsolete, in the Royal Navy and the United States Navy for a person employed by the captain to keep his records, correspondence, and accounts. The regulations of the Royal Navy demanded that a purser serve at least one year as a captain's clerk, so the latter was often a young man working his way to a purser's warrant. He had high status, with an office on the quarterdeck or upper deck on most ships. He was paid at the same rate as a midshipman in 1800, but by 1815 he had almost the same monthly pay as a standing warrant officer. On large ships, he had his own cabin in the gunroom, but on smaller vessels he lived with the midshipmen on the orlop deck.
Once commissioned, a ship required a great deal of paperwork to keep her in good order. The recognized office staff consisted of captain's clerk, the purser, and the purser's steward. On most ships the first lieutenant was allowed a "writer" to help him draw up the watch and station bills, chosen from among the most literate landmen, otherwise the paperwork was done by the officers themselves. Occasionally the clerk had clerk's assistants, similar to how most warrant officers had mates.
In order to have his accounts passed at the Admiralty, a captain had to present at least 25 different completed books and forms. Some were quite simple, such as a copy of his commission, others were complex, such as the two copies of the log book or the muster book which had to be sent periodically. The main job of the captain's clerk was to prepare these documents, and to copy out the general correspondence of the captain. The captain's clerk worked closely with the purser, especially regarding the muster book which was used to determine how much to feed the crew.