In April 1967, USAF began fitting its entire EC-121 fleet with QRC-248 IFF transponder interrogators. QRC-248 had been developed to follow Soviet -export aircraft flown by the Cuban Air Force. The SRO-2 transponders installed in Soviet export MiGs enabled Cuban ground-controlled interception (GCI) radars to identify and control their fighters. A testbed EC-121 called "Quick Look" had flown with College Eye in January 1967 to test QRC-248 and found that North Vietnamese MiGs used the same transponder. QRC-248 accurately discriminated MiG radar returns from the myriad returns picked up during a mission and extended the range of low-altitude detection to more than 175 miles, covering virtually all important North Vietnamese target areas.