dress coats, left, four-button fatigue (“sack”) coats, right.

As Lewis Foster noted on May 17, 1864, the men in his company traded in their dress coats, like the one at left, piped in artillery red, for looser fitting four-button fatigue (“sack”) coats, right. (Heritage Auctions, Dallas; ©Don Troiani.
All Rights Reserved 2022/Bridgeman Images)