Into the summer of 1863, the Confederate army led by Lee played for keeps by sending a sizable contingent towards North, as much as Pennsylvania. It clashed because of the Union army at Gettysburg, where the biggest battle ever become battled on American soil occurred. After three days of hopeless fight, the Confederates must admit their defeat. At Gettysburg, the Potomac military Union artillery contributed to support the Confederate advance, impacting the results of this battle.