Upon the evacuation of Yorktown, the III Corps led the pursuit of the retreating enemy, attacking them at Williamsburg on May 5, with Hooker's and Kearny's Divisions. This battle was fought almost entirely by the III Corps; of the 2,239 casualties on that field, 2,002 occurred within its ranks; and three-fourths of them in Hooker's Division, the brunt of the battle having fallen on the Excelsior Brigade and Jersey Brigade, both in Hooker's command. Porter's Division was not engaged, having been left at Yorktown; on May 18, the new V Corps was created with Porter in command, his old division was detached from the III Corps to serve in the new outfit, leaving only two divisions, Hooker's and Kearny's, in the corps, and reducing its aggregate strength to 23,331 present and absent, with 34 pieces of field artillery. The two divisions numbered about 17,000 effectives, out of the 18,205 reported as "present for duty".