leaving out quite a bit of historical facts on purpose from the original webpage aren't we now? Why doesn't that surprise me? You are so busted....
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The P-51D/K introduced the K-14 computing gyro gunsight, based on a British (Ferranti) design
http://home.att.net/~jbaugher1/p51_10.html
In the summer and autumn of 1944 four major improvements incorporated in Spitfire fighter variants at that time deserve special mention in this account. In order of thier entry into service they were: the installation of the gyro gunsight, the fitting of the 'E' Type wing and armament, the fitting of the bubble canopy, together with a redesigned and cut-back fuselage, and the installation of additional fuel tanks iin the rear fuselage. These Modifications greatly increased the fighting ability of the Spitfire.
: Late Mark Spitfire Aces 1942–45 - Alfred Price - Osprey puplishing
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The Gyro gunsight;
In action the effectiveness of a fighter's cannon and machine guns depends on the pilot's ability to aim the rounds with sufficient accuracy to score hits on the target. During the mid-war period RAF fighters carried simple GM2 reflector gunsights. This provided an illuminated fixed aiming point in the centre of the reflector glas, surrounded by a fixed circle which helped the pilot judge the correct deflection angle when engaging a manouvering crossing target. In fact the ability to judge the deflection angle accurately in the heat of the battle was the main points that seperated the ace pilots from the also-rans. Early in the war it was realised that if an automatic device could be developed to indicate to the pilot the correct amount of deflection to use when firing during a turning combat, this would greatly enhance the effectiveness of the fighter force.
: Late Mark Spitfire Aces 1942–45 - Alfred Price - Osprey puplishing
http://en.wikipedia.org/wiki/Gyro_gunsight