to respond to the aircraft before it flew out of range. This was effective against interceptor aircraft but of little use against surface-to-air missiles (SAMs), whose attack times were measured in seconds. This led to the adoption of low-level attacks, where the bombers would fly below the radar horizon so they could not be seen on ground-based radars. Quail, originally designed for the high-altitude mission, was modified with the addition of a barometric altimeter to allow it to fly at lower altitudes. Doing so seriously limited its effective range and flight time. In the early 1960s, the Air Force began to question the usefulness of Quail in the face of improving Soviet defenses. SRAM Looking for another solution to the Soviet SAM problem, in 1964 the Air Force began developing a new system that would directly attack the missile sites rather than confuse them. This emerged as the AGM-69 SRAM, with a range of about , allowing it to be launched from outside the roughly range of the SA-2 Guideline missiles it faced. Flying at Mach 3, it quickly flew out in front of the bombers, reaching the missile site before the bomber flew into the range of the SA-2. While highly capable against known missile locations, SRAM could do nothing to defend against unknown sites, nor help with the problem of interceptor aircraft. To deal with these threats, Quail continued to be carried, typically in pairs, providing some defense against these other threats. However, by the late 1960s the Air Force concluded "that the Quail was only slightly better than nothing." SCAD In January 1968, a new requirement emerged for a modern version of Quail for this new mission, the Subsonic Cruise Aircraft Decoy, or SCAD. SCAD was designed specifically to fit onto the same rotary launcher used by SRAM, allowing a single aircraft to carry multiple SRAM and SCAD and launch either at any time. This led to it being the same length as SRAM, and the use of a fuselage with a triangular cross-section, which maximized the usable volume on the rotary launchers. The system was otherwise similar to Quail, using a simple inertial navigation system (INS) allowing the missile to fly a pre-programmed course. Soon after development began, it was noted that the very small nuclear warheads being developed at that time could be fit to SCAD without seriously affecting its performance as a decoy. This