Spear was born in Weymouth, Dorset and entered the Royal Navy in 1779, joining the 74-gun as a midshipman. The "Marlborough" was commanded at this time by Captain Taylor Penny, also from Weymouth, and a previous acquaintance was probably responsible for Spear obtaining a position on the ship. "Marlborough" was one of the ships assigned to the fleet under Sir George Brydges Rodney and sent to relieve Gibraltar in early 1780. Spear's ship was in action several times within a few months, firstly at the interception and capture of a convoy of Spanish ships of the Caracas Company on 8 January, and then at the Battle of Cape St. Vincent on 16 January. "Marlborough" was then detached with a small squadron under Admiral Robert Digby and ordered to escort a convoy to Menorca. While returning to Britain from Gibraltar, Digby's squadron came across the French 64-gun "Protée", escorting a fleet of transports bound for Mauritius. The "Protée" and three transports were duly captured.