 On 31 December 1943 , Eisenhower and Montgomery first saw the plan , which proposed amphibious landings by three divisions and two @-@ thirds of an airborne division . The two generals immediately insisted that the scale of the initial invasion be expanded to five divisions , with airborne <unk> by three divisions , to allow operations on a wider front . The change doubled the frontage of the invasion from 25 miles ( 40 km ) to 50 miles ( 80 km ) . This would allow for quicker <unk> of men and materiel , make it more difficult for the Germans to respond , and speed up the capture of the port at Cherbourg . The need to acquire or produce extra landing craft and troop carrier aircraft for the expanded operation meant that the invasion had to be delayed to June . 
