John G. Nicolay, The Outbreak of Rebellion

With such professions of a fighting spirit, the Administration looked with some confidence for an offensive campaign, and sent its best regiments and officers to take part in it. Both General Scott and General Patterson were, however, deceived in their expectation that the rebels meant to risk a battle at that point. With a total force of something over seventeen regiments, Patterson at length began his forward movement via Hagerstown and Williamsport. But so leisurely were his preparations and advance, that the rebels had every knowledge of his coming; and when, on June 15th, he finally reached the Potomac River, he found, instead of the “desperate resistance” which had been looked for, that Johnston had hastily evacuated Harper's Ferry after destroying the railroad bridge and spiking his heavy guns, and had retreated upon Winchester.

Patterson and his officers were greatly mystified by this withdrawal of the enemy. “I believe it is designed for a decoy,” wrote Fitz John Porter, Chief of Staff, to Cadwalader, second in command. “There may be a deep-laid plot to deceive us.” “The whole affair is to me a riddle,” wrote Cadwalader back to Porter. Advancing with a painful overcaution, as if Johnston were the invader, a part of the army crossed the Potomac on the 16th of June.

Finding the rumor of the evacuation true, Patterson took sufficient courage to report a victory. “They have fled, and in confusion,” he wrote. “Their retreat is as demoralizing as a defeat; and, as the leaders will never be caught, more beneficial to our cause. Harper's Ferry has been retaken without firing a gun.”

“What movement, if any, in pursuit of the enemy, do you propose to make, consequent on the evacuation of Harper's Ferry?” asked General Scott by telegraph. “Design no pursuit; cannot make it,” replied Patterson. That determination