At the height of the French and Indian War the General Court of Connecticut appointed Doolittle Armourer (or Armorer) of the Connecticut Militia: in 1755, he served on the General Staff under General William Johnson from June 9 to August 6 and from September 10 to December 6, supporting Connecticut's war effort. He was again appointed Armorer in 1758, this time for Connecticut's Fourth Regiment under Colonel David Wooster. As armorer "he gained some experience in gunpowder production", which would prove vitally important to the Patriot war effort during the American Revolutionary War twenty years later. He designed an innovative nested bateau or lake boat for the 1755 amphibious attack on Fort Carillion and saw the construction of the "Land" "Tortoise," a floating gunboat, skills he would use two decades later in the American Revolution. He also gained firsthand knowledge of British leadership incompetence in the disastrous expedition against Fort Carillon as well as their superior naval capabilities in the successful Siege of Louisbourg of 1758.