abortive start of Operation Cobra on July 24 with Lieutenant Generals Courtney Hodges and Lewis H. Brereton. They were forced to take shelter as errant American bombs dropped around them. Lieutenant General Lesley J. McNair invited Simpson to watch the repeat of the bombardment with him the following day, but Simpson elected to return to his headquarters in England. Once again bombs fell short, and McNair was killed. The Ninth Army headquarters moved to France, as it landed at Utah Beach on August 29 and 30. It became active as part of Lieutenant General Omar Bradley's 12th Army Group on September 5, when it took over command of the US forces in Brittany from Lieutenant General George S. Patton Jr.'s Third Army. Simpson's first task was the capture of Brest. To overcome strong natural and man-made defenses, Simpson chose to employ overwhelming firepower. There were sufficient artillery pieces in the area, but not sufficient ammunition, especially for the heavier pieces. Over a two-week period, of artillery ammunition was brought forward from dumps in Normandy and the UK. The battle commenced on September 8, and after much hard fighting the city was liberated on September 20, 1944. Simpson moved his headquarters to Arlon, where it opened on October 2, and two days later the Ninth Army relieved First Army in the southern portion of its line, taking over the center of the 12th Army Group's front in the Ardennes between the First and Third Armies. The stay at Arlon was brief; on October 10, Simpson received word that Ninth Army was to take over the northern sector of the 12th Army Group's front adjoining Field Marshal Bernard Montgomery's Anglo-Canadian 21st Army Group. This was a consequence of Eisenhower's decision to reinforce that sector. The plan was for the Ninth Army to envelop the Ruhr industrial area to the north while First Army enveloped it to the south. Reflecting on the decision later, Bradley opined that the "uncommonly normal" Ninth Army staff collaborated with the 21st Army Group better than the more temperamental First Army staff did. Ninth Army's attack on the Siegfried Line north of Aachen commenced on November 16, heralded by artillery and aerial bombardment that included attacks by heavy bombers of the Eighth Air Force and RAF Bomber Command. Progress was slow and costly. Simpson's offensive ended on December 14, but on the Roer River rather than the Rhine,