On September 19 at the Battle of Chickamauga, Bragg began an unsuccessful attempt to interpose his army between Rosecrans and Chattanooga before the arrival of most of Longstreet's corps. Throughout the day, Confederate troops launched largely unsuccessful assaults on Union positions that were highly costly for both sides. One of Longstreet's own divisions under Hood successfully resisted a strong Union counterattack from Jefferson C. Davis's division of the XX Corps that afternoon. When Longstreet himself arrived on the field in the late evening, he failed to find Bragg's headquarters. He and his staff spent considerable time riding looking for them. They accidentally came across a federal picket line and were nearly captured. When the two finally met at Bragg's headquarters late at night, Bragg placed Longstreet in command of the left wing of his army; Lt. Gen. Leonidas Polk commanded the right. On September 20, Longstreet lined up eight brigades in a deep column against a narrow front, an attack very similar to future German tank tactics in World War II. The attack was supposed to begin early in the morning shortly after an assault by Polk's wing. However, confusion and mishandled orders caused Polk's attack to be delayed, and Longstreet's advance did not begin until just after 11 after hearing gunfire from his left. By chance, a mistaken order from General Rosecrans caused a gap to appear in the Union line by transferring Thomas J. Wood's division from the right to reinforce the XIV Corps under George Henry Thomas in the center.