due to the flooding threat posed by Roer dams upstream. The Urft Dam (Urfttalsperre) held of water, and the Rur Dam (Schwammenauel) held another . The Germans could demolish them to create a disastrous flood. Alternatively, through controlled demolition, they could release . This would put the river into a flood condition that would cause it to rise by , increase the speed of the current by and increase the width to . This would preclude a crossing attempt for ten to twelve days. Eisenhower was anxious about accepting an army commander without operational experience in the war, but senior officers with such experience were few in May 1944. By October 1, however, Eisenhower was sufficiently impressed by Simpson's performance to write to the Chief of Staff of the Army, General George C. Marshall, and recommend that Simpson's temporary rank of lieutenant general be made substantive. According to Colonel Armistead D. Mead, Simpson's G-3 (Operations) officer: During the crisis of the Battle of the Bulge, the Ninth Army came under Montgomery's command on December 20. The Ninth Army took no part in the battle, but was stripped of eight divisions to reinforce the First Army, and took over part of its front. After the battle was over in early 1945, the Ninth Army remained with Montgomery's 21st Army Group for the final attack into Germany. For Operation Grenade, the crossing of the Roer, the Ninth Army was reinforced, its strength increased from five to twelve divisions. The major obstacle to the advance was the river itself, as the dams were still in German hands. The British Second Army commenced Operation Veritable, the northern part of a pincer movement to clear the Rhineland, on February 8, 1945. Montgomery's plan was for Operation Grenade, scheduled to commence on February 10, 1945, to form the southern part of the pincer, but there was still no word of the capture of the Roer dams by the First Army. Montgomery left the decision of whether to delay Operation Grenade up to Simpson, but postponement would make the task of both the British troops already fighting more difficult, and increase the risk that the Germans would detect the Ninth Army's preparations. Simpson watched the river slowly rise, but could not be certain whether it was the result of German demolition or increased flow due to snow melt. Finally, he postponed the attack. His decision was the