A number of factors contributed to the reduced emphasis on the interdiction strategy. Three, however, appear to have most influenced the inauguration of Operation PRESSURE, the name given the new policy of concentrating aerial attacks on major industrial targets considered of greatest value to the North Korean economy. Mounting FAF aircraft losses due to enemy flak (fire from ground-based antiaircraft weapons) and an insufficient number of replacements helped shape the new program. By April 1952 FEAF had received “only 131 replacement aircraft of the types engaged in rail interdiction against the 243 it had lost and the 290 major-damaged aircraft on interdiction sorties.”[93] These heavy losses had resulted from the increasing accuracy of Communist antiaircraft ground weapons, a capability Air Force planners had failed to consider sufficiently.[94] [93] USAF, _Ops in Korea_, No. 72, p. 156. [94] Futrell, _USAF, Korea_, pp. 436–437. Although significant, this loss factor was not the final consideration in executing PRESSURE attacks against the power plants. More directly responsible were two other recent developments. These were the decision of the new UN commander, General Mark W. Clark, to take forceful action to bring the Communists around to an armistice agreement and a top-level Defense Department change of policy that had removed a major North Korean hydroelectric facility from the restricted bombing list. This was the Suiho plant, fourth largest in the world. Adjacent to the Yalu River, about 75 miles northeast of its mouth, Suiho supplied approximately 25 percent of the electrical power used in nearby northeast China.[95] [95] _Ibid._, pp. 452–453 and Cagle and Manson, _Sea War, Korea_, pp. 443–445. Results of the PRESSURE strikes, carried on from 23–27 June, were highly successful. Marine, Navy, and Air Force planes flew 1,654 attack and escort sorties in these raids. Of the 13 target plants attacked during this period, 11 were put out of commission and 2 others were presumably destroyed. North Korea was almost blacked out for two weeks. Chinese and Russian experts were rushed to North Korea to lend a hand in restoration. The hydroelectric strikes marked the first time that Marine, Navy, and Air Force pilots had flown a combined mission in Korea. The 23 June strike, moreover, was of particular significance to 1st MAW since it was also the first time that MAGs-12 and -33 were assigned group strikes at specific adjacent targets at the same time. Led by Colonel Robert E. Galer, the new MAG-12 commander since 25 May, group pilots struck and leveled the single power complex, Chosin 3, in the 23–24 June runs. Colonel John P. Condon, who had taken over MAG-33 on 24 May, put 43 jets from VMFs-311 and -115 into the air during the two-day mission. The first time that its F9Fs had ever been massed for a strike of this type, the MAG-33 jets similarly destroyed the Chosin 4 plant, 11 miles northwest of Hamhung.