William Swinton, Campaigns of the Army of the Potomac

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[129] march. Now, it was almost simultaneous with the establishment of the base at White House that McDowell's column was turned aside from its contemplated co-operation with the Army of the Potomac, and diverted to the Shenandoah Valley. Knowing this fact, General McClellan knew that the hope of further re-enforcements was vain, and it was incumbent on him to act vigorously with his proper force. He knew that the presence of Jackson's corps in the Shenandoah Valley neutralized a force of fifteen thousand men that was certain to be brought against him if he should delay. Besides, he was making an offensive movement in which vigorous action was above all requisite; for when once the offensive has been assumed, it must be sustained to the last extremity. Yet, having reached the Chickahominy, he assumed an almost passive attitude, with his army, too, cut in twain by that fickle and difficult stream.

Now, though a position á cheval on a river is not one which a general willingly assumes, it is frequently a necessity, and in that case he spans the stream with numerous bridges.¹ It was necessary for General McClellan to pass the Chickahominy because it crossed his line of manoeuvre against Richmond; and it was also necessary for him to leave a force on the eastern side to cover his communications with his base at the White House; but this is not a situation in which one would assume a passive attitude with few and very imperfect connections between the divided wings. The passage of the Chickahominy was made by Casey's division at Bottom's Bridge on the 20th of May, and by the 25th the corps of Keyes and Heintzelman were established on the right bank. Meantime, the corps of Sumner, Porter, and Franklin remained on the left bank. By the 28th, Sumner had constructed two bridges² for the passage of his corps; but