Shrike. If the aircraft fired a missile, the Shrike could be neutralized with the side-pointing technique without sacrificing any S-75s. Another tactic was a "false launch" in which missile guidance signals were transmitted without a missile being launched. This could distract enemy pilots, or even occasionally cause them to drop ordnance prematurely to lighten their aircraft enough to dodge the nonexistent missile. At the same time, evasive maneuvers were used, and intensive bombardments of identified SAM firing positions were organized. Under these conditions, camouflage and radio silence became especially important. After combat launches, an anti-aircraft missile division was to leave the area immediately, otherwise it would be destroyed by a bombing attack. Until December 1965, according to American data, eight S-75M systems were destroyed, although sometimes American aircraft bombed dummy positions equipped with decoy missiles made of bamboo. Soviet and Vietnamese calculations claimed the destruction of 31 aircraft; the Americans acknowledged the loss of 13 aircraft. According to the memoirs of Soviet advisers, on average an anti-aircraft missile unit destroyed 5-6 American aircraft before being put out of action. Despite these advances, the US was able to come up with effective ECM packages for the B-52E and later models. When the B-52s flew large-scale raids against Hanoi and Haiphong over an eleven-day period in December 1972, 266 S-75 missiles were fired, resulting in the loss of 15 of the bombers and damage to numerous others. The ECM proved to be generally effective, but repetitive USAF flight tactics early in the bombing campaign increased the vulnerability of the bombers and the North Vietnamese missile crews adopted a practice of firing large S-75 salvos to overwhelm the planes' defensive countermeasures (see Operation Linebacker II). By the conclusion of the Linebacker II campaign, the shootdown rate of the S-75 against the B-52s was 7.52% (15 B-52s were shot down, 5 B-52s were heavily damaged for 266 missiles). However, some of the U.S aircraft which "crashed in flight accidents" in fact were lost due to S-75 missiles. When landing at an airfield in Thailand, one B-52 that had been heavily damaged by a SAM rolled off the runway and exploded on mines installed around the airfield to protect from the guerrillas; only one crewman survived. Subsequently, this B-52 was counted as "crashed in flight accidents". According to Dana Drenkowski and Lester W. Grau, the number of U.S. aircraft confirmed by themselves as lost is