The fewer pieces a pattern, the less abstract it is to look at. Such is the case with the field shirt, with its one-piece Dolman sleeve. This is an entirely seam-free upper body, save for a spine up the back. It makes for a very relaxed fit — excellent layering potential— with the cloth draping over the shoulder.
The split of the upper and lower body inherent to this type of construction creates the opportunity for a couple of chest pockets. It'd be churlish to refuse. The front also has a laid-on placket, a shirt collar, and a collar-latch in memory of field shirts and CPO shirts of military yore.