Complex sentence: By 11:30 a.m., Union forces had reached the Confederate main line and at about 1:00 p.m., they took the crest while the troops from Carter L. Stevenson's division retired in disorder.
Split into simpler sentences: By 11:30 a.m., the Union forces had reached the Confederate's main line. At 1:00 p.m., they took the crest, the troops from Carter L. Stevenson's division retiring in disorder.