Two of the biggest missing pieces in the RailWorks British steam locomotive fleet. (https://en.m.wikipedia.org/wiki/WD_Austerity_2-8-0) (W.D. 2-8-0) (https://www.flickr.com/photos/andrew_bradford/36522370885) (W.D. 2-10-0) Engines of war, akin to the likes of the Austerity Hunslets, S100, S160 (but propably better) and the Kriegsloks. After WW2, many got scattered across the world, so, similarly to the S160, the potential for variations is high.
