Looking for lower-cost options, a number of studies carried out between 1965 and 1967 examined a variety of scenarios where a limited number of interceptors might still be militarily useful. Among these, the I-67 concept suggested building a lightweight defense against very limited attacks. When the Chinese exploded their first H-bomb in 1967, I-67 was promoted as a defense against a Chinese attack, and this system became Sentinel in October. Nike-X development, in its original form, ended. Soviet development of ICBMs decreased the value of the Nike (aircraft) air defense system. Beginning around 1965, the number of Nike batteries was reduced. Thule air defense was reduced during 1965 and SAC air base defense during 1966, reducing the number of batteries to 112. Budgetary cuts reduced that number to 87 in 1968, and 82 in 1969. Some small-scale work to use Nike Zeus as an anti-satellite weapon (ASAT) was carried out from 1962 until the project was canceled in favor of the Thor based Program 437 system during 1966. In the end, neither development would enter service. However, the Nike Zeus system did demonstrate a hit to kill capability against ballistic missiles during the early 1960s. See National Missile Defense and anti-ballistic missile systems. Nike Hercules was included in SALT I discussions as an ABM. Following the treaty signed during 1972, and further budget reduction, almost all Nike sites in the continental United States were deactivated by April 1974. Some units remained active until the later part of that decade in a coastal air defense role. These trucks and trailers were used with the Nike system. By 1958, the Army deployed nearly 200 Nike Ajax batteries at 40 "Defense Areas" within the United States (including Alaska and Hawaii) in which Project Nike missiles were deployed. Within each Defense Area, a "Ring of Steel" was developed with a series of Nike Integrated Firing and Launch Sites constructed by the Corps of Engineers. The deployment was designed to initially supplement and then replace gun batteries deployed around the nation's major urban areas and vital military installations. The defense areas consisted of major cities and selected United States Air Force Strategic Air Command bases which were deemed vital to national defense. The original basing strategy projected a central missile assembly point from which missiles would be taken out to prepared above-ground launch racks ringing the defended area. However, the Army discarded this semimobile concept because the system needed to be ready for instantaneous action to fend off a "surprise attack." Instead, a fixed-site scheme was devised.