Frustrated in his attempt to outflank the Confederate defenders along the Warwick River at Lee’s Mill on April 5, 1862, Maj. Gen. George B. McClellan decided instead to besiege the Rebel lines. He ordered gun emplacements built between the James and York Rivers outside of Yorktown and brought up heavy artillery. On April 16, at Dam No. 1 on the Warwick, Union infantry probed the Confederate defenses, now under the command of Gen. Joseph E. Johnston, and were pushed back. McClellan was convinced he was outnumbered and that any attack would be futile. For two weeks, he planned a massive artillery bombardment preparatory for an infantry assault to take place early on May 4. Before McClellan’s big guns could fire, Johnston slipped away from his Yorktown defenses and moved to Williamsburg, where McClellan attacked him on May 5.