II (AAM-N-3/AIM-7B). After Douglas dropped out of this program, Canadair continued on with it until the termination of the Arrow project. The AAM-N-3 Sparrow II was unique in that it had a fully active radar guidance system. This combined both a radar transmitter and receiver in the missile, making it unnecessary for the pilot to keep the aircraft aimed at the target after firing the missile, unlike Semi-active radar homing (SARH) missiles which require continuous radar-assisted guidance throughout flight. This allowed the aircraft that fired the AAM-N-3 to turn away, prosecute other targets, and/or escape from potential retaliatory missiles fired by the enemy aircraft during the time it takes for the Sparrow to reach its target. Despite the significant advantages of this design over SARH guidance, all subsequent models of the Sparrow use semi-active radar homing. To accommodate the active radar guidance system, the AAM-N-3 Sparrow II had a much greater volume than its predecessor. Its size would subsequently set the precedent for all future Sparrow variants. In 1959, Canadair had completed five missiles based on airframes from Douglas, and built two models from scratch, when the program was cancelled with the cancellation of the Arrow. Italy The Italian company Finmeccanica (now Leonardo S.p.A.), Alenia Difesa licensed the AIM-7E Sparrow technology from the US, and produced its own version. Later in the 1980s, Alenia started to produce an improved version of the AIM-7 called the Aspide, compared to the AIM-7E, it received a newer and improved monopulse guiding system that allowed for a better hit ratio and easier targeting of enemies at low altitude confused in the ground clutter. It also received a new and more powerful engine and new control surfaces, these control surfaces were all independent one of the others, this gave the missile a much better maneuverability compared to the AIM-7E and the English Skyflash that still used dependent control surfaces. People's Republic of China The PL-11 and HQ-6 is a family of Chinese missiles developed by the Shanghai Academy of Science and Technology, largely based on the Italian Aspide missile – a version of the Sparrow. Soviet Union The Soviet Union acquired an AIM-7 in 1968 and a Vympel team started copying it as the K-25. The missile did not enter production as the R-23 was thought to have better versatility, range, signal processing logic, and immunity from interference. K-25 work ended in 1971, but analysis