 Complete the following phrase:  The effectiveness of heat-seeking missiles was only 7 early in the Vietnam War, but improved to approximately 1540 over the course of the war. The AIM-4 Falcon used by the USAF had kill rates of approximately 7 and was considered a failure. The AIM-9B Sidewinder introduced later achieved 15 kill rates, and the further improved AIM-9D and J models reached 19. The AIM-9G used in the last year of the Vietnam air war achieved 40. Israel used almost totally guns in the 1967 Six-Day War, achieving 60 kills and 10 losses. However, Israel made much more use of steadily improving heat-seeking missiles in the 1973 Yom Kippur War. In this extensive conflict Israel scored 171 of 261 total kills with heat-seeking missiles 65.5, 5 kills with radar guided missiles 1.9, and 85 kills with guns 32.6. The AIM-9L Sidewinder scored 19 kills out of 26 fired missiles 73 in the 1982 Falklands War. But, in a conflict against opponents using thermal countermeasures, the United States only scored 11 kills out of 48 fired Pk  23 with the follow-on AIM-9M in the 