I was wondering when the Pinkerton unit would show up.
Edwin C. Fishel's "The Secret War for the Union: the Untold story of Military Intelligence in the Civil War"
Is an excellent resource for most things relating to early and middle war Union intelligence. Fishell spent 30 years in US intelligence services starting with the OSS of WW2. In 1959 he found a roomful of never before seen secret Union intelligence documents. He spent the next 30 years collecting more info for his book.
The book goes into great detail about Pinkerton and his operations and dispells many myths, both dealing with Pinkerton and with southern espionage supremacy.
Fishell's conclusion is that Pinkerton skewed his number to match what Mac wanted, and not the other way. For whatever reason Mac truly believed the Rebs had 200,000 although no other intelligence could prove it.
Pinkerton should be tied into McClellan, as he was hired by Little Mac and moved on when Little Mac did. The problem with Pinkerton is that his agents dealt mainly with strategic intelligence. They were dispatched to Richmond and only collected information on the AoNV when passing through or by Richmond rumors.
Many Pinkerton agents were caught. I'm interested to see how the game handles the espionage aspect. It can really be tricky to pull off and hard to please everyone. I'm just thankfull it is included.
Even if it is not 100% historically acurate, it should add another fun dimension to the game.
Historical background.
McClellan practically blinded himself by disassembling his cavalry brigades to serve menial task such as orderlies, couriers, guards, etc..
Also, McClellan was the sole clearing house for any intelligence gathered by the Army. He had no staff to investigate or collate the information.
After McClellan, Gen Pope made an agressive push to collect intelligence by ordering his commanders to hire as many spies and agents as possible. The problem was these agents were in lower-middle Virginia or the Valley, when the campaign moved north, Pope was blind, hence 2nd Manassas.
Burnside made almost no attempt to gather intell.
It was Gen Joe Hooker that created the Union Cavalry Corps and the first actual intelligence section on an army staff. It was the precursor to modern, all source, staff based intelligence gathering and analysis. It was this organization that discovered Lee had almost no troops west of Fredericksburg, and allowed Hooker to move 5 Union Corps onto Lee's flank undetected.
So why the Union debacle at Chancellorsville? Hooker sent Stonemans cavalry on a deep raid to cut Lee's rail lines, depriving himself of battlefield "eyes" when he needed them the most.
That's as much as I've read so far...
(as you can tell, I really like this book
)
Pinkerton was McClellan incognito and visa versa. They were just missing the Third Stooge to become hilariously historic. They had to wait for Butler but Butler never made it to the picnic. 
