A lack of sufficient transport aircraft meant that 1st Airborne Division would be dropped in three separate lifts over three successive days. 1st Parachute Brigade and most of 1st Airlanding Brigade would land on 17 September, 4th Parachute Brigade and the rest of 1st Airlanding Brigade would land on 18 September, and on 19 September the Polish 1st Independent Parachute Brigade would land, along with a supplies for the entire division. The division would use approximately 650 gliders during the operation, of which 39 would be Hamilcars. It appears that the Hamilcars that had been used by 6th Airborne Division and subsequently abandoned in June had been replaced, as records state that 64 of the gliders were available by September. Thirteen Hamilcars would be flown on 17 September and land in landing zone 'Z'. Eight of the gliders would carry 17-pounder anti-tank guns, their towing vehicles and crews, and the other five would carry ten Universal Carriers, two apiece; the Carriers were to act as transports for the airborne troops. On 18 September fifteen Hamilcars would land in landing zone 'X'; eight would carry a 17-pounder anti-tank gun, their towing vehicles and crews each, and the other four would carry eight Universal Carriers, which would once again act as transport for the airborne troops that were flown in. The final three were packed with ammunition and stores, as well as a number of sappers from the Royal Engineers; these were experimental loads, as it was believed that the Hamilcar might be a more efficient way of transporting supplies rather than the Horsa due to its larger size. On 19 September, ten Hamilcars would transport American engineers who belonged to the American 878th Aviation Engineer Battalion and their equipment, which included bulldozers, cranes and graders; they were to construct a forward airfield in landing zone 'W' after the gliders had been cleared away.