On 16 December 1944, at the start of the Battle of the Bulge, Montgomery's 21st Army Group was on the northern flank of the allied lines. Omar Bradley's US 12th Army Group was to Montgomery's south, with William Simpson's US Ninth Army adjacent to 21st Army Group, Courtney Hodges' US First Army, holding the Ardennes and George S. Patton's US Third Army further south.