Before developing the Green Mace gun, the British worked on two projects called “Longhand” and “Ratefixer“. These were 94mm anti-aircraft guns designs in which it was intended to increase the rate of fire and the caliber to meet the threat of modern aircrafts. Although the missiles were beginning to appear it was necessary to cover the gap until future arrival of such weapons.The QF 127/58 SBT X1 Green Mace gun was an impressive weapon, with 8 meters in length and 28 tons of weight. The gun was mounted on a towable 3-axle chassis, that did not offer good off-road performance. That is why the use of this gun should have been limited to protection of high-value targets as command centers and HQs. However, despite its huge size, the gun was fired by a single person who sat in a similar glass cabin to those installed in mobile cranes.The gun achieved a firing rate of 96 shells per minute, which is quite an achievement for a weapon of this caliber. The problem was that the two ammunition drums, (on the image), only contained 14 shells each, so at maximum rate of fire, could only fire for 18 seconds. Reloading this gun was a very cumbersome process that took between 10 and 15 minutes. This slowness was counterproductive and greatly limited the effectiveness of Green Mace.Green Mace fired sub-calibrated projectiles of 4.8 kg at an effective distance of 7,600 meters. At more distance the effectiveness of the ammunition decreased considerably. The muzzle velocity was 1,200 m/s, really high for an anti-aircraft gun and its rate of fire was exceptionally high when compared to the effective German anti-aircraft guns of the WWII.It is unknown if Vickers company came to finish a prototype of the 127mm Green Mace. Anyway, in 1957 the project was canceled due to the operational complexity of this large gun. In addition, the lack of effectiveness of the 102mm barrel did not help either. The amount of vehicles needed for each battery it would have been a huge investment. For this very reason, it would have been impossible to obtain a sufficient number of batteries to have an effective defense. Furthermore, missiles were already beginning to demonstrate their enormous anti-aircraft capabilities.
