Maker "JM" subcontractor to EOC?

[Darkman]

This 13 Pr 9 cwt AA case I believe was made by "JM" as a subcontractor to the large EOC works.
Is this correct and who was JM?

Thanks, Graeme

 

[Snufkin]

The J/M in a diamond is not a manufacturer but an inspector's mark of the manufacturer Armstrong Whitworth (EOC) - akin to the anchor stamp seen on Kynoch cases, the anchor being an Inspector's mark of that company.

 

[Darkman]

OK thanks. Being so large and close to the EOC I thought it a subcontractor, similar to when a square is used. Cheers

 

[Snufkin]

OK thanks. Being so large and close to the EOC I thought it a subcontractor, similar to when a square is used. Cheers

The JM marking is often placed close to the EOC monogram, above or below it, but is also found at random locations on the case head. The attached shows the JM inspection mark below the Lot identifier, and I have also seen it placed to the left of the case 18pr identifier.