A deep water harbour was needed

The principal key of success in this huge operation would be to provide supplies to the allied armies.

They needed a fonctional deep water harbour immediately.
CHERBOURG harbour was chosen.

LE HAVRE was not retained because it would have been too difficult to resist to the powerful 15th german army stationed with their famous Panzer Tank Division just near PAS DE CALAIS. 

A necessity : UTAH BEACH

 The geographical shape of the Cotentin along with large flooded areas by the germans would make the capture of CHERBOURG very difficult with a heavy loss of human life beginning at OMAHA BEACH.

Landing on UTAH BEACH would prove to be vital.