achieved the first AA kill against these targets in 1933. In March 1936, six Queen Bee targets were destroyed by the RN Mediterranean Fleet during intensive AA practice at a time of extreme tension between the UK and Italy. Target practice against target drones was carried out using special shells which were designed to minimize the possibility of destroying expensive targets. The RN allowed media coverage of AA target practice and a 1936 newsreel has footage of an actual shoot. In 1935 the RN also began to practice HACS controlled shoots of target aircraft at night. Tachometric and radar additions The RN moved quickly to add true tachometric target motion prediction and radar ranging to the HACS by mid 1941. The RN was the first navy to adopt dedicated FC AA radars. However the system, in common with all World War II-era mechanical AA fire control system still had severe limitations as even the highly advanced United States Navy (USN) Mk 37 system in 1944 needed an average of 1,000 rounds of ammunition fired per kill. In 1940 the Gyro Rate Unit (GRU) was added to the HACS system, an analogue computer capable of directly calculating target speed and direction, converting the HACS into a tachymetric system. Also in 1940, radar ranging was added to the HACS. The GRU and its associated computer, the "Gyro Rate Unit Box" (GRUB) no longer assumed straight and level flying on the part of the target. GRU/GRUB could generate target speed and position data at angular rates of up to 6 degrees per second, which was sufficient to track a crossing target at a range of . The Fuze Keeping Clock RN destroyers were hampered by the lack of good dual-purpose weapons suitable for ships of destroyer size; for much of the war 40° was the maximum elevation of the guns equipping such ships, which were consequently unable to engage directly attacking dive bombers, although they could provide "barrage" and "predicted fire" to protect other ships from such attacks. Destroyers did not use HACS, but rather the Fuze Keeping Clock (FKC), a simplified version of HACS. Starting in 1938 all new RN destroyers, from the onwards, were fitted with a FKC and continuous prediction fuse setting trays for each main armament gun. WWII experience from all navies showed that dive bombers could not be engaged successfully by any remote computer-predictive AA system using mechanical