To attack this force, even after Jackson’s arrival, was to court disaster.  The right was protected by the Chickahominy, the left rested on White Oak Swamp, a network of sluggish streams and impassable swamps, screened everywhere by tangled thickets.  It needed not the presence of the siege ordnance, placed on the most commanding points within the lines, to make such a position absolutely impregnable.

North of the Chickahominy, however, the Federals were less favourably situated.  The Fifth Army Corps, 25,000 strong,* (* The Fifth Army Corps included McCall’s division, which had but recently arrived by water from Fredericksburg.  Report of June 20, O.R. volume 11 part 1 page 238.) under General FitzJohn Porter, had been pushed forward, stretching a hand to McDowell and protecting the railway, in the direction of Mechanicsville; and although the tributaries of the Chickahominy, running in from the north, afforded a series of positions, the right flank of these positions, resting, as Stuart had ascertained, on no natural obstacle, was open to a turning movement.  Furthermore, in rear of the Fifth Corps, and at an oblique angle to the front, ran the line of supply, the railway to West Point.  If Porter’s right were turned, the Confederates, threatening the railway, would compel McClellan to detach largely to the north bank of the Chickahominy in order to recover or protect the line.

On the north bank of the Chickahominy, therefore, Lee’s attention had been for some time fixed.  Here was his adversary’s weak point, and a sudden assault on Porter, followed up, if necessary, by an advance against the railway, would bring McClellan out of his intrenchments, and force him to fight at a disadvantage.  To ensure success, however, in the attack on Porter it was necessary to concentrate an overwhelming force on the north bank; and this could hardly be done without so weakening the force which held the Richmond lines that it would be unable to resist the attack of the 75,000 men who faced it.  If McClellan, while Lee was fighting Porter, boldly threw forward the great army he had on the south bank, the rebel capital might be the reward of his resolution.  The danger was apparent to all, but Lee resolved to risk it, and his audacity has not escaped criticism.  It has been said that he deliberately disregarded the contingency of McClellan either advancing on Richmond, or reinforcing Porter.  The truth is, however, that neither Lee, nor those generals about him who knew McClellan, were in the least apprehensive that their over-cautious adversary, if the attack were sudden and well sustained, would either see or utilise his opportunity.

From Hannibal to Moltke there has been no great captain who has neglected to study the character of his opponent, and who did not trade on the knowledge thus acquired, and it was this knowledge which justified Lee’s audacity.

The real daring of the enterprise lay in the inferiority of the Confederate armament.  Muskets and shot-guns, still carried by a large part of the army, were ill-matched against rifles of the most modern manufacture; while the smooth-bore field-pieces, with which at least half the artillery was equipped, possessed neither the range nor the accuracy of the rifled ordnance of the Federals.