Longstreet was unjustly blamed for not attacking earlier in the day, on July 2, 1863, at Gettysburg. I can answer that criticism, as I know more about the matter than the critics. If he had attacked in the morning, as it is said he should have done, he would have encountered Buford’s division of cavalry, five thousand sabres, on his flank, and my corps would have been in his front, as it was in the afternoon. In a word, all the troops that opposed Longstreet in the afternoon, including the Fifth Army Corps and Caldwell’s division of the Second Corps, would have been available on the left flank of the Union army in the morning. Every regiment and every battery that fired a shot in the afternoon was on the field in the morning, and would have resisted an assault in the morning as stubbornly as in the afternoon. Moreover, if the assault had been made in the morning, Law’s strong brigade of Alabamians could not have assisted in the attack , as they did not arrive on the field until noon. On the other hand, if Lee had waited an hour later, I would have been on Cemetery Ridge, in compliance with General Meade’s orders, and Longstreet could have marched, unresisted, from Seminary Ridge to the foot of Round Top, and might, perhaps, have unlimbered his guns on the summit.
General Meade’s telegram to Halleck, dated 3 P.M., July 2, does not indicate that Lee was then about to attack him. At the time that dispatch was sent, a council of corps commanders was assembled at General Meade’s headquarters. It was broken up by the sound of Longstreet’s artillery. The probability is that Longstreet’s attack held the Union army at Gettysburg. If Longstreet had waited until a later hour, the Union army might have been moving towards Pipe Creek, the position chosen by General Meade on June 30.
Source: Lee and Longstreet at High Tide
Commentary
Daniel Sickles, who commanded the Third Corps, Army of the Potomac at Gettysburg, and James Longstreet became close friends after the war, often exchanging letters and making sure to see one another when near each other. Upon Longstreet's death, his wife Helen completed writing and published a book about her husband called Lee and Longstreet at High Tide. Its subject matter was, in part, her husband's role at Gettysburg.
Before publication, Helen asked Dan Sickles to write the preface to the book. Following is a part of that preface: