The air campaign mounted against North Vietnam was the first time that an integrated air defense system based around radar-controlled guns and surface-to-air missiles had been encountered. Proponents of surface-to-air missiles had claimed that their lethality would drive manned aircraft from the battlefield. At first, the U.S. Air Force was hard-pressed to neutralize North Vietnam's radar-controlled defenses, but did prevail. Electronic countermeasures support for the air war against North Vietnam included stand-off jamming, Wild Weasel operations, the use of self protection pods, and the employment of chaff. Using all these techniques, Linebacker II saw the B-52s of Strategic Air Command facing the most effective air defense system the Soviet Union could provide. The B-52s won; the much-heralded surface-to-air missiles were scoring a lower kill rate than German defenses in World War Two. This campaign laid the foundations for the technology used by the USAF to neutralize enemy defenses ever since.