The 1st Engineer Battalion, commanded by Lieutenant Colonel John H. Partridge, was given the mission by Corps of jamming the gates of the dam at the open position. Compliance would have to wait, of course, until the KMCs took the dam. Partridge conferred meanwhile with Colonel Bowser, and it was decided to take no action after the anticipated capture until a demolitions reconnaissance could be made.[155] [155] BrigGen A. L. Bowser, ltr of 14 Feb 58; Col J. H. Partridge, ltr of 17 Mar 58. As early as 18 April a KMC patrol had crossed the Pukhan into the town of Hwachon, which was found abandoned except for 11 Chinese soldiers, who were taken prisoner. Marine engineers installed a floating bridge on the 21st for the advance of one KMC battalion the next morning. The other two battalions were to cross the river several miles downstream by DUKWs.[156] [156] CO KMC Regt msg to CG 1stMarDiv, 2335 22 Apr 51, in KMC In&Out #1; Col C. W. Harrison, _Narrative_, Mar-Apr 51. Corps plans for the attack were made in full realization of air reconnaissance reports for 20 and 21 April indicating that the enemy offensive buildup was in its final stages. This intelligence was gleaned in spite of all enemy efforts to frustrate the airmen. CCF spotters were placed on mountain tops to give the alarm, and relays of men fired shots to pass on warnings of approaching planes. Antiaircraft defenses were increased at such vital spots as bridges and supply areas. The Communists even went so far as to put out decoys--fake trucks, tanks, and tank cars--to lure UN fighter-bombers within range of antiaircraft guns. These efforts resulted in 16 Marine planes being shot down from 1 to 21 April 1951. Nine of the pilots were killed, one was captured, three were rescued from enemy territory, one walked back to friendly outposts, and two managed to bail out or crash-land behind the UN lines.[157] [157] Compilation of data from 1stMAW sqdn _HD_s, Apr 51; _PacFlt Interim Rpt_ No. 2, II, 1051, 1071. This total was equivalent to two-thirds of the average tactical squadron. Because of the disruption to the 1st MAW pilot replacement program, the Commandant arranged for 20 pilots to be flown to Korea to augment the normal rotation quotas.[158] [158] _Ibid._ Direct opposition from enemy aircraft was also on the increase. CCF flights even reached the EUSAK battle line as unidentified light planes flew over positions or dropped small bombs. Evidently the enemy was using well camouflaged airfields in North Korea. An air battle took place on 20 April when two VMF-312 pilots from the _Bataan_, Captain Philip C. DeLong and First Lieutenant Harold D. Daigh, encountered four YAK fighters in the heavily defended Pyongyang-Chinnanpo area. They gave chase and shot down three of the enemy planes.[159] [159] 1st MAW _HD_, 20 Apr 51; VMF-312 _HD_, 20 Apr 51.