The records were transferred to the Museum by arrangement with the Admiralty in 1938. They consist of 5,205 volumes, 1673 to 1809. In some cases captains' logs have been bound with those of lieutenants, but they are usually duplicates of those at the Public Record Office, which holds the series of captains' and masters' logs for this period and ships' logs from 1799. Some expense accounts for paper and ticket books are also bound in with the logs. Although this is a very full series of records it is not always certain that a log will exist for a particular commission; a detailed index of the logs by ship is kept in the Manuscripts Section.

Administrative / biographical background
The lieutenants' logs were kept by the lieutenants of a ship in commission, recording details of weather, navigation and the routine of the ship, as well as incidents that occurred during the commission. Printed formats appeared from about 1799, different printed forms being sold by various printers in Portsea and in Plymouth. A standard form was laid down by the Admiralty in October 1805 when the practice of starting the day's log at noon was altered to coincide with the civil calendar, by beginning the log at midnight. At the completion of each year a lieutenant's log was required to be deposited in the Admiralty Office, accompanied by a certificate stating that the officer had complied with the printed instructions and not been absent from his ship. At the Admiralty the chief clerk abstracted details of the voyage and, in return for a fee, sent the log to the Navy Office where a clerk in the office of the Clerk of the Acts made out a certificate entitling the lieutenant to be paid. At the Navy Office individual logs were bound into volumes. It was the practice to bind them according to the name of the ship, not that of their keeper, but during a period in the mid-eighteenth century logs were collected by year, as well as by name of ship, and logs for four or five ships, beginning with the same letter, were bound in one volume.