On the 24th May 1864 Grant gifted Lee the kind of opportunity that rarely happens in a campaign: to wreck the other’s army.
After the bloodletting of May 5-12th, that cost Lee 22000 casualties and Grant 34000,'weakening both armies by 33% and 25% respectively, Grant again disengaged and moved South towards Richmond. Lee had followed and had been reinforced with 7 small Brigades from his capital.
Grant had inadvertentally straddled his large army across the North Anna river.
Lee saw the way to take advantage of his smaller numbers and punish the Federal II Corps, Grant’s best. He could throw 30000 men at the 24000 that were over the V in the river separating Grant’s two halves of his army. Hancock’s 24000 could not be reinforced, because of the V of the river, so he readied his assault.
On the afternoon of the 24th Lee fell violently sick with diarrhoea. He lay helplessly for hours while the opportunity to assault, before the Union commanders realised the sure situation were in.
The reason Lee’s defensive strike could not be undertaken was simple: the attrition of the last 19 days had robbed him of a subordinate able to manage it.
Time and opportunity passed. Grant and Hancock’s isolated Corps were extremely lucky.
We all know the loss of a quarter of Grant’s force would never have changed his resolve to “fight it all out, even if it takes all Summer”, but another battering would have diminished his potential to do so sooner.