at dawn on september 17 , maj. gen. joseph hooker 's corps mounted Process_start a powerful assault Attack on lee 's left flank .

at a crucial moment , confederate maj. gen. a. p. hill 's division arrived Arriving from harpers ferry and launched Process_start a surprise counterattack Attack , driving Preventing_or_letting back burnside and ending Process_end the battle Hostile_encounter .

although he was being pursued Self_motion at a leisurely pace by maj. gen. george b. mcclellan 's army of the potomac , outnumbering Expansion him more than two to one , lee chose Choosing the risky strategy of dividing Cause_to_amalgamate his army and sent Sending one portion to converge Come_together and attack Attack harpers ferry from three directions .

jackson methodically positioned Placing his artillery around harpers ferry and ordered Request maj. gen. a.p .

the mission was assigned Choosing to the 1st brigade combat Hostile_encounter team of the 4th infantry division , commanded Control by maj. gen. raymond odierno and led Conquering by col. james hickey of the 4th infantry division , with joint Collaboration operations task force Hostile_encounter unk elite and covert joint Collaboration special operations team .