In the 1960s, the Sterling company began to worry about the prospects of continued sales of the Sterling (Patchett) SMG, especially in light of new competitors like the H&K MP5. Its chief design engineer, Frank Waters, created the S11 as a gun to replace the classic Sterling. The S11 was based on a simple stamped/folded steel receiver, and was intended to have a lower unit cost that the Sterling. It kept the excellent Patchett magazine, but had a barrel and sights offset to the left side, and offered two separate bayonet lugs – one for the No5 rifle and one for the L1A1/FAL.
Unfortunately for Sterling, it was determined that the tooling cost would have made the S11 actually more expensive that the existing guns, whose tooling costs had been long since covered. Also, the S11 was just not a very good or very reliable design – a “donkey in a thoroughbred race” to quote one Sterling manager. This one prototype was the only example ever made, and the project was shelved in 1967 in favor of expanding into more civilian models of the original Sterling.
Many thanks to the Royal Armouries for allowing me to film and disassemble this one of a kind submachine gun! The NFC collection there – perhaps the best military small arms collection in Western Europe – is available by appointment to researchers. You can browse the various Armouries collections online here.