One of many "blurbs" online.....
This version had no folding wings. Since the aircraft were not deemed fit for carrier operations there was no need for folding wings, and so the construction and weight of the folding system was saved. Also, this version had a clear-view canopy that in itself improved the pilot’s fields of vision but, more importantly, had a domed top that allowed the seat to be raised by some 7 in (0.18 m) for a useful improvement in the pilot’s forward fields of vision. Also, a pneumatic rather than solid tire on a heightened tailwheel unit was introduced, that effectively lowered the nose, and a small spoiler was added on the leading edge of the starboard wing. The 862nd F4U-1A introduced another upgraded feature in the form of 1 × Pratt & Whitney R-2800-8W radial with a water-injection capability that boosted maximum power to 2,250 hp (1.678 kW).
Number built: 2,066
So the "true" -1 has no WEP