Gavin was part of Mission Boston on D-Day. This was a parachute combat assault conducted at night by the US 82nd Airborne Division on June 6, 1944, as part of the American airborne landings in Normandy. The intended objective was to secure an area of roughly on either side of the Merderet River. They were to capture the town of Sainte-Mère-Église, a crucial communications crossroad behind Utah Beach, and to block the approaches into the area from the west and southwest. They were to seize causeways and bridges over the Merderet at La Fière and Chef-du-Pont, destroy the highway bridge over the Douve River at Pont l'Abbé (now Étienville), and secure the area west of Sainte-Mère-Église to establish a defensive line between Gourbesville and Renouf. Gavin was to describe the operation as having two interrelated challenges – it had to be 'planned and staged with one eye on deception and one on the assault'.