"At first the kilt was used as a fatigue garment, made from worn-out plaids, but as it was so much more convenient and comfortable that by the time of the American War it had supplanted the plaid on all but the most formal occasions."
-from 18th Century Highlanders (Osprey #261); Stuart Reid/Mike Chappell, 1993

The belted plaid was the formal, "dress uniform" garment after the philabeg came into army use ca. 1758, as one of Lord Howe's innovations....