The
HS.831A is a post-war development of the
HS.830 developed in 1944, which is a scaled-up version of the 20 mm
HS.820 and has much the same general operating principles. Originally, the 30×170mm brass case round was developed, it was later changed to a steel case round. The HS.831A was initially used in combination with the
HS.661A, a single simple anti-aircraft gun mount, which was quickly supplemented by the
HS.661B mount with much better fire control and smooth traverse, making maximum use of the practical range potential. The HS.831A was also mounted on the
AMX-13 DCA 30, a
self-propelled anti-aircraft weapon for the
French Army, as well as the
AMX-30 DCA (another
self-propelled anti-aircraft weapon) for the
Saudi Arabian Army. In the United Kingdom,
BMARC developed A32, a locally operated naval mounting incorporating two HS.831. When the gun was renamed KCB, the A32 became
GCM-A series. And LSE (Laurence, Scott & Electricmotors Ltd; presently MSI Defence Systems) also developed a single mount for KCB, which became
DS30B. Both GCM-A and DS30B were introduced by the
Royal Navy. The
30 mm Rarden was developed based on the 30×170mm round that this gun used, but it wasn't interchangeable due to the KCB round using a steel case instead of a brass one. The
United States Navy designated the twin HS.831 weapons system developed by
Emerson Electric as
EX-74., which was officially classified as the
Mark 74 gun mount. This mount was never used by the USN widely, but commercialized as the
Emerlec 30 (or
EE-30) and purchased by foreign navies (such as
South Korean Navy,
Nigerian Navy and
Greek Navy). ==Variants==