I haven't messed with AACW in a few years, but playing the board game For the People inspired me to reinstall. I'm obviously a bit out of the loop, but have patched up to 1.16a.
I'm playing the Union in the +Kentucky full campaign. It's turn 8, late July '61, and I just discovered that generals can combine with single brigades, which combinations are then named after the brigade. There appear to be stringent restrictions on the combos. Multiple brigades grouping is apparently not allowed, which along with the grayed out Form Division button tells me that these are not divisions. There's also a popup stating the limitations.
What is this ability? What are the benefits and when was it implemented? I printed the manual years ago, but find no reference to unit combinations smaller than divisions.