Logistics During World War II, Operation Grenade was the crossing of the Roer river between Roermond and Düren by the U.S. Ninth Army, commanded by Lieutenant General William Hood Simpson, in February 1945, which marked the beginning of the Allied invasion of Germany.

On 9 February, the U.S. Ninth Army—operating under Field Marshal Bernard Montgomery's Anglo-Canadian 21st Army Group since the Battle of the Bulge—was to cross the Roer and link up with the Canadian First Army, under Lieutenant-General Harry Crerar, coming from the Nijmegen area of the Netherlands in Operation Veritable, which had started at 05:00 on 8 February.

It had been anticipated that the Germans would try to do this, and that General Omar Bradley's U.S. 12th Army Group could capture them in time to stop the flooding.

During the two weeks that the river was flooded, Hitler would not allow Generalfeldmarschall Gerd von Rundstedt to withdraw behind the Rhine, arguing that it would only delay the inevitable fight.

German forces west of the Rhine during operations Veritable, Blockbuster and Grenade lost 90,000 men, of which more than 50,000 became prisoners of war (POW).