Critics of McClellan I have conversed with often trot out the argument "Grant would have attacked", so lets test that. I propose the following hypothesis:
"Grant would have made a major assault (on the 18th) the day after having made a major assault".
My methodology is to examine all Grant's assaults where the enemy remained on the field the next day. If the hypothesis is true then we will find major assaults the day after major assaults.
Major Assaults by Grant
- Vicksburg: assault on the 19th May 1863 (3 days after Champion Hill)
- Vicksburg: assault on the 22nd May (3 days after previous, no follow up)
- Spotsylvania: assault on the 10th May 1864
- Spotsylvania: assault on the 12th May
- Spotsylvania: assault on the 18th May
- North Anna: assault on the 23rd May
- Cold Harbor: assault on the 1st June
- Cold Harbor: assault on the 3rd June
- 2nd Petersburg: assault on the 16th June
- 2nd Petersburg: assault on the 18th June
- Jerusalem Plank Road: assault on the 21st June
- Crater: assault on the 30th July
- 2nd Deep Bottom: assault on the 14th August
- Globe Tavern: assault on the 18th August
- Chaffin's Farm; assault on the 30th September
- Peeble's Farm: assault on the 30th September
- Peeble's Farm: assault on the 2nd October
- 2nd Fair Oaks: assualt on the 27th October
- Boydton Plank Road: assault on the 27th October
- Hatcher's Run: assault on the 7th February 1865
- Fort Stedman: assault on the 25th March
Thus given the fact that out of 21 tests Grant did not immediately repeat the attack 21 times I think we can dismiss this canard.
Conclusion: Grant would NOT have attacked at Antietam on the 18th September 1862, as per the other 21 times he was faced with similar situations. He likely would have prepared himself for a day or two for another effort (like Vicksburg, Spotsylvania and Cold Harbor).
Probability of Grant not attacking, assuming a free choice of whether or not to attack = 99.99995%
(Derived as 1- (0.5)^21)