In order to reinforce and expand the D-Day bridgeheads won on 6 June 1944, the Allies needed a port to bring in troops and vital supplies. Cherbourg was therefore the first priority for the American VII Corps after the D-Day Landings of 6 June 1944. After establishing a firm beach-head, elements of VIII Corps, under the command of Major-General J. Lawton 'Lightning Joe' Collins, moved west across the base of the Cotentin Peninsula to isolate the 40,000-strong Cherbourg garrison, dug in behind concrete and field fortifications in dominating hill positions. Collins then sent divisions north to Cherbourg, but maintained units facing south as well to prevent any German reinforcement. Cherbourg's capture was highlighted by a violent storm that had raged since 19 June, crippling Allied landing vessels. On 22 June three American divisions began their assault on Cherbourg, supported by air attacks and naval bombardment. A bitter six-day street-to-street battle ensued, as the German commander had been ordered to hold the port to the last. The last German forces in Cherbourg surrendered on 29 June, after thoroughly destroying the harbour facilities. The port would not be usable for months.