I always thought the DR boots with a 3-buckle flap came in black, and often see e-bay listings for the 2-buckle brown Officer boots listed incorrectly as DR boots. But here is a pair of 3-buckle brown boots- earlier pattern predating the black more common pattern? Curious. E-bay # 281321352563
A friend of mine had a pair of 1916 dated boots, almost identical to the WW2 black 3 buckle ones but of one piece construction (no separate toe cap), it seems they were Royal Engineer issue, so perhaps that's where the idea came from?
