Thomas Earnshaw's Marine Chronometer No.509 was manufactured around 1800 and served on a number of Royal Navy ships. William Edward Parry while exploring Baffin Bay in July 1819 during his first attempt to find the Northwest Passage mentions that Earnshaw's chronometer had been used in 1818 to determine the longitude of a spot to within of his own measurement. He does not, however, say which ship it was on board. At this early time, all Royal Navy purchased chronometers were issued by the Greenwich Observatory who also checked their rates and sent them out for cleaning between voyages. Initially, Greenwich issued chronometers directly to ships, but later, as chronometers became more common, they were sent from Greenwich to other Royal Navy ports and dockyards for issue locally. The first recorded issue from Greenwich was 3 July 1823 to Captain Frederick Marryat in command of HMS Larne. Larne took part in the First Anglo-Burmese War which lasted from 1824 to 1826. The chronometer was returned to Greenwich 6 February 1826 and then sent to its makers for servicing. It did not come back to Greenwich for nearly two years. On 4 March 1828 it was issued to Captain J. Bolder in command of HMS Hecla. At this time Hecla was a famous ship: under the command of George Francis Lyon she had been part of Parry's second expedition to find the Northwest Passage. Over 6,000 members of the public visited the ship at Deptford while she waited to set out on Parry's third expedition in 1824. The attempt ended in 1825 after the leading ship, HMS Fury was abandoned due to ice damage. Parry used Hecla again in an 1827 attempt to reach the North Pole. Parry unwillingly gave up Hecla when the admiralty sent her to survey the West African coast under the command of Bolder. In July 1830 the chronometer was returned from Hecla and went for cleaning to Robert Molyneux in London. It was returned to Greenwich in November but not immediately issued to another ship.Lincoln P. Paine, "HMS Hecla", Ships of the World: An Historical Encyclopedia, pp.237-238, Houghton Mifflin Co., 1997 Portsmouth and Devonport In March 1831 the chronometer was delivered to Devonport where the rate was checked and recorded. On 6 December 1831 it was issued to Captain Stokes in command of HMS Beagle. It sailed with Captain Fitzroy on Beagles famous second voyage and was