 In 1804 he was appointed first lieutenant of the third rate  ("Billy Ruffian" to her crew).Her commander, Captain John Cooke, and Cumby had an especially close professional relationship, so when the ship lined up in Admiral Collingwood's division on 21 October 1805 in the opening stages of the battle of Trafalgar, Cooke made the unusual move of taking Cumby and the ship's master Edward Overton into his confidence about the ship's orders and Admiral Nelson's confidential instructions; in case something should happen to him, the ship would still have able, informed direction.Once action was joined, "Bellerophon" rapidly found herself sandwiched between the Spanish and the French , both pouring fire into the British.