"Read up on The Battle of the Crater"

Specially trained USCT were supposed to spearhead the assault. They were replaced at the last minute by white troops because the high command DIDN'T want to be perceived as use the USCT as cannon fodder in what promised to be a costly assault - as were most assaults on entrenched positions. The USCT were sent in after the first wave, but the situation was already botched and the whole affair became a slaughter.

"When the ANV went into Maryland in '62 Ewell's Corps had over 3000 black soldiers in the ranks. Not teamsters and cooks but rifle toting soldiers."

First of all, Richard Ewell had a division, not a corps, in the Maryland Campaign. It was in Jackson's corps, but was commanded by Alexander Lawton since Ewell lost his leg at Second Bull Run. Second, Jackson's corps mustered some 7,700 men in two divisions on the morning of September 17, 1862 in the area around the Cornfield and East Woods, one of which was Ewell’s; D.H. Hill was at the Sunken Road and A.P. Hill was marching from Harper's Ferry. [See Stephen Sears, “Landscape Turned Red: The Battle of Antietam,” pp. 181-182 (Ticknor & Fields, NY 1983)] Not having a breakdown of the numbers handy, I will assume for argument’s sake that Ewell’s division made up half of that number. That means that 1) Ewell had a 75% black division that neither he nor anyone else in the ANV or Army of the Potomac mentioned; 2) the 3,000 blacks had been detached to parts unknown; or 3) Ewell did not have 3,000 black soldiers in the ranks. Considering that 3,000 black soldiers in Confederate uniform in the thick of the fighting around the Cornfield and East Woods probably would have drawn comment from someone and Lee wouldn’t have let 3,000 reinforcements just sit on their hands, option 3 seems most likely.