[Postwarden]

An article in The Formation Sign Journal of the Military Heraldry Society published in October 2020 sheds further light on this photo.

Between the wars the four Territorial battalions of the Royal Warwickshire Regiment continued to wear on their service dress the system of coloured shapes they had worn in the first World War and that shown in the original photo posted is probably the vertical dark blue rectangle worn by the Warwicks 8th Bn.

The 6th Bn wore a similar red vertical rectangle but in 1936 as part of the rebuilding of Britain's AA defences the 6th Bn was converted to 69th Anti-Aircraft Bn (Royal Warwickshire), Royal Artillery (its HQ in Birmingham) which adopted Artillery cap and collar badges - but retained the red rectangle on the arm as this picture proves.

The rectangles were worn until the introduction of battle dress which was not announced until March 1939, initial issues going first to the Regular Army from that summer. Many units went to France in 1939 wearing service dress which lingered on for quite some time.

Jon