Part of the Confederate line bulged outward; this part was soon called the "Mule Shoe". On May 12, Grant attacked the Mule Shoe with several thousand men. The Union attack captured part of the Confederate line but Confederate commander Robert E. Lee sent reinforcements to counterattack. The fighting lasted all day at the Mule Shoe. By the end of the day, an oak tree almost two feet wide was completely severed by all the rifle fire.