The Andrews machine carbine was developed by Birmingham Small Arms on behalf of an Australian client, a Mr. Andrews, who designed the weapon. It was a particularly eccentric submachine gun which placed great emphasis on compactness. The receiver was in a rectangular shape with a folding pistol grip and spare mag carrier in the rear. When slotted into its carrier, the spare mag acted as the buttstock. The actual magazine from which the gun fired was horizontally loaded into the left side of the receiver. The internal action was also unusual. It operated on the blowback principle but the bolt was carried by two spring-loaded guide rods passing above and below the chamber (these can be seen to partially protrude on either side of the muzzle).
The Andrews gun was submitted to the Ordnance Board in 1943 and was considered a weapon of interest, despite being a privately-funded venture. It was put forward into the submachine gun trials of September/October 1943 where it was tested against the Patchett, Welgun, Sten Mk.IVB, Austen Mk.II, and Owen Mk.II. It failed to impress against the superior Owen and Patchett designs and was criticized for being of fragile build and uncomfortable ergonomics. No further action was taken with the Andrews gun, but the designer apparently came to Britain later to work at RSAF Enfield.