The modified version XX (MK 20) of Merlin engine was introduced in 1940. The new two speed supercharger allows the pilot to change the impeller speed according to the altitude (air pressure). At 18000 feet or above, the pilot can turn to high-speed transmission ("FS ratio" - full supercharge) to increase compression. Below 18000 feet, the pilot can turn to low-speed transmission ("Ms ratio" - normal supercharge), which will reduce the consumption of engine power. As a result, it can provide greater power at different heights, and the performance of the engine has been significantly improved, with a maximum output of 1280 horsepower.On june11,1940, the first hurricane MK I equipped with grey backed Falcon XX made its maiden flight. In September, 1940, when the British air war was the most intense, hurricane MK iia1 also began to be delivered to all flight squadrons.Hawk aircraft company has sufficient experience in refitting fighter aircraft. In the first test, two Oerlikon contracts 20mm anti-aircraft guns were installed under the hurricane wing with pods, but the amount of ammunition carried was small, and the design of ammunition supply by the bomb drum often had the situation of jamming. Finally, four Hispano Mk II 20mm aerial guns were installed in the wing.The performance of the grey backed Falcon XX is so good that old hurricanes can still be produced. Hawk aircraft company soon launched hurricane MK iia2, one equipped with 12 bailangling machine guns and the other with 4 Hispano aerial guns. The first MKII A2 was delivered in October with a larger propeller.Later named MK IIB and MK IIC, they were launched in April and June 1941, respectively, with slightly modified wings. The new wing is equipped with a bomb rack, which can hang 250 kg, 500 kg bombs or additional fuel tanks. At this time, the performance of Germany's new fighters had surpassed that of hurricanes, so the role of hurricanes turned to fighter bombers and night fighters.Mk II was also used for g