War Department (UK) 30 ft van. Not based on any specific prototype so just for fun, although the WD did use standard railway company designs. Original photo texture from Chris Whiting who retains copyright.reskin of John Whelan's mesh.
Thanks to andi06 for his superscript, which runs the ACS and Chris Nawlins for working it out.
It has two levels of LOD and culls both the bogeys and ACS couplings so should be performance friendly.