Most of Gen. Joseph E. Johnston's army was not on the peninsula on April 4th when Maj. Gen. George B. McClellan departed Fortress Monroe on his Peninsula Campaign. The only force opposing the Yankee advance up the peninsula toward the Confederate capital at Richmond was Maj. Gen. John B. Magruder’s small force of two divisions at Yorktown behind the Warwick River. Magruder’s deceptive theatrics, conspicuously parading his men back and forth behind his defenses, convinced the Federals that his works were strongly held by an entire, much larger army. McClellan suspended the march toward Richmond, ordered the construction of siege fortifications, and brought his heavy guns to the front. In the meantime, Gen. Joseph E. Johnston brought reinforcements for Magruder. On April 5th, Union forces probed for a weakness in the Confederate line at Lee’s Mill, and again on April 16th at Dam Number 1. Failure to exploit the initial successes of these attacks, however, held up McClellan for two additional weeks, while he considered other options to outflank the Warwick Line. With his big siege guns finally in place, McClellan planned for a massive bombardment to begin at dawn on May 4th, but the Confederate army had slipped away in the night toward Williamsburg.