 During the Seven Years' War, Cook served in North America as master aboard the fourth-rate Navy vessel .With others in "Pembroke"s crew, he took part in the major amphibious assault that captured the Fortress of Louisbourg from the French in 1758, and in the siege of Quebec City in 1759.Throughout his service he demonstrated a talent for surveying and cartography and was responsible for mapping much of the entrance to the Saint Lawrence River during the siege, thus allowing General Wolfe to make his famous stealth attack during the 1759 Battle of the Plains of Abraham.