Great Western Short Coaches

There are several designs to consider. First those with a guard's duckets or a space where one may have been. These are easily distinguished as the T20/T21 designs did not have a separate guard's door whereas the T38/T39 did.
Diagrams T20 and T21 LA9N	28'6 long 19' wheelbase	JN Slinn collection courtesy of John Lewis
Diagrams T38 and T39 LA9N	31' long 9'6 x 9'6 wheelbase	R Spratt collection JN Slinn collection
Then there are those designs without a guard's duckets or a space where one may have been. These are harder to distinguish. The S5 can just be distinguished from the U11/U12 as the panels between the compartment windows are slightly narrower. The compartments in the U15/U16 and U21 are wider than the S5 and U11/U12 and so the panels between the windows are still wider. U21 can be differentiated from the others as the eaves panels are 3" deeper. Also to be considered is diagram U20 which should be Lewis style LE12CN, but some LA12B coaches appear to have kept their single arc roof when converted and so fit in here. That makes U20 and U21 indistinguishable without seeing there running number.
Diagram S5 LA9N	28' long 9'6 x 9'6 wheelbase	courtesy of John Lewis
Diagrams U11 and U12 LA9N	28'6 long 18' wheelbase	R Spratt collection
Diagrams U15 and U16 LA9N	31' long 9'6 x 9'6 wheelbase	© GWR
Diagram U20 LE12CN	31' long 19' wheelbase	JN Slinn collection © HC Casserley 96341
Diagram U21 LA12N	31' long 9'6 x 9'6 wheelbase	© L&GRP 6367 JN Slinn collection