A12 Ammunition boxes were originally designed to transport the charges for the Livens Projector, a type of mortar designed specifically to fire gas shells. As it became clear these were not going to be needed, these were no longer needed.
It appears the only contractor for these boxes was Electrolux Ltd in Luton. All surviving boxes are marked ELX to indicate this. Unfortunately the modern company has no surviving records of any wartime work.
The Aux Units packs were put together at Aston House which also provided stores for SOE. It seems they had links to the nearby Electrolux company to supply ammunition boxes as a number of stores appear in them. In a history of Aston House, one of the workers recalled filling A12 boxes with these packs for Auxiliary Units in November 1941. Another document from Kent records the accidental issue of a Mk1 pack and that it was indistinguishable from a Mk2 from the outside, confirming both were packed in the same boxes and that most likely they had no markings.
Creating replica packs has revealed that the large A12 box was essential to contain all the components. Few other boxes could contain as much equipment. Deep Bronze Green seems to be the original colour found on surviving boxes.
At some point in 1943, the A12 presses were modified to produce an even larger box by making the sides taller. It is not known if this was to meet an SOE requirement. Surviving boxes were mainly used as travel trunks by post-war servicemen. These boxes do not have the A12 stamp on the lid.
A12 boxes still come up for sale from time to time though they are uncommon. Typical price is around £20-£30 but varies according to condition.