Cook's first posting was with HMS Eagle, sailing with the rank of master's mate. In October and November 1755 he took part in Eagles capture of one French warship and the sinking of another, following which he was promoted to boatswain in addition to his other duties. His first temporary command was in March 1756 when he was briefly the master of the Cruizer, a small cutter attached to the Eagle while on patrol.
In June 1757 Cook passed his master's examinations at Trinity House, Deptford qualifying him to navigate and handle a ship of the King's fleet , He then joined the frigate HMS Solebay as master under Captain Robert Craig.
During the Seven Years' War, he served in North America as master of Pembroke . In 1758 he took part in the major amphibious assault that captured the Fortress of Louisbourg from the French. Cook then participated in the siege of Quebec City before the Battle of the Plains of Abraham in 1759. He showed a talent for surveying and cartography and was responsible for mapping much of the entrance to the Saint Lawrence River during the siege, allowing General Wolfe to make his famous stealth attack on the Plains of Abraham.
Cook's surveying skills were put to good use in the 1760s, mapping the jagged coast of Newfoundland. Cook surveyed the northwest stretch in 1763 and 1764, the south coast between the Burin Peninsula and Cape Ray in 1765 and 1766, and the west coast in 1767. Cook’s five seasons in Newfoundland produced the first large-scale and accurate maps of the island’s coasts; they also gave Cook his mastery of practical surveying, achieved under often adverse conditions, and brought him to the attention of the Admiralty and Royal Society at a crucial moment both in his personal career and in the direction of British overseas discovery. Cook's map would be be used into the 20th century, copies of it being referenced by those sailing Newfoundland's waters for 200 years.
Following on from his exertions in Newfoundland, it was at this time that Cook wrote, he intended to go not only:
"... farther than any man has been before me, but as far as I think it is possible for a man to go"
