During King William's War, De Lahontan submitted several proposals for military fortification and equipment in New France such as a Great Lakes Flotilla for defense against the Iroquois and a line of forts meant for defence along the western frontier, both on behalf of Governor Frontenac in 1692. Further, he led a successful offense against five English frigates of Phipp's invasion fleet in the Gulf of St. Lawrence in 1690 under Frontenac. Though his proposal for a Great Lakes flotilla was ultimately rejected on the basis of cost, de Lahontan would be promoted to King's Lieutenant.