Though helicopters were initially armed merely as defensive measures to support the landing and extraction of troops, their value in this role lead to the modification of early helicopters as dedicated gunship platforms. Though not as fast as fixed-wing aircraft and consequently more vulnerable to anti-aircraft weaponry, helicopters could use terrain for cover, and more importantly, had much greater battlefield persistence owing to their low speeds. The latter made them a natural complement to ground forces in the CAS role. In addition, newly developed anti-tank guided missiles, demonstrated to great effectiveness in the 1973 Yom Kippur War, provided aircraft with an effective ranged anti-tank weapon. These considerations motivated armies to promote the helicopter from a support role to a combat arm. Though the U.S. Army controlled rotary-wing assets, coordination continued to pose a problem. During wargames, field commanders tended to hold back attack helicopters out of fear of air defenses, committing them too late to effectively support ground units. The earlier debate over control over CAS assets was reiterated between ground commanders and aviators. Nevertheless, the US Army incrementally gained increased control over its CAS role.