Following his defeat at Gaines Mill, McClellan decided the withdraw further, and shift his base to the James river. This required crossing White Oak Swamp where Lee, guessing his intention intended to trap and destroy the Yankees. While his other divisions marched south east to head the Union army off, Magruder and Jackson were to assult their rear. Jackson again failed to show up and when Magruders division encountered the Union rearguard at around 5pm on the 29th, a fierce artillery duel ensued accompanied by several Confederate attacks, all of which were repulsed by a well organised and led defence. A thunderstorm at about 9pm halted the battle but the Union defence had bought plenty of time for the slow wagon train to get out of the area.