At the age of 11 years and 8 months, on 6 August 1757, he took on the role of captain's servant (then a standard route into a commissioned rank) on the newly built HMS Burford, where he served until October 1758.
[1] After a brief respite, presumably in the company of his family, he returned to active duties in March 1776, stationed in what was then the critical location of North America, under Lord Howe.
[1] He returned to England briefly, marrying Ann Grace Kinchin of Stoke Charity on 16 March 1780 at Deane, Hampshire before being redeployed in October 1780 again to the West Indies.
In April 1782 he received a post of first lieutenant under Lord Howe on HMS Victory and was subsequently present at the Great Siege of Gibraltar in October of that year, where he commanded the fireship Pluto as part of the attack.
In 1797 he therefore became deeply embroiled in the Nore Mutiny and was part of the prosecution and execution of its ringleader Richard Parker, both of which took place on board Mosse’s ship.
The British government erected a joint monument to Mosse and a second naval hero, Edward Riou, who also fell in the Battle of Copenhagen, in the crypt of St Paul's Cathedral in London.