There was no adequate system of alerting these air defense stations to the effect that planes were departing or incoming. Many of them failed to send out their standard identification friend or foe (IFF) signals; and those that did so were still suspect, since U.S. electronics equipment on UN planes had fallen into enemy hands. As a consequence MGCIS-1 was kept busy vectoring air defense fighters to verify that certain bogeys were friendly transports, B-29s, or enemy bombers.[136] [136] _PacFlt Interim Rpt_ No. 2, II, 1038, 1039. A “bogey” is an unidentified plane. In an effort to cope with the situation, General Harris requested that another Marine ground control intercept squadron, MGCIS-3 be sent to Korea. He desired that Marine Air Control Group-2 (MACG-2) also be made available to coordinate the Wing’s air control functions. These units sailed on 5 March from San Francisco. Until March 1951 the Air Force’s 606th Aircraft Control and Warning Squadron had participated in the air surveillance of the Pusan area from the top of 3,000-foot Chon-San--the encroaching mountain that made K-9’s traffic pattern so hazardous. This Air Force unit displaced to Taejon early in March, and the MGCIS-1 commanding officer, Major H. E. Allen, moved his radio and radar vans to the mountain top to take over the job.[137] [137] LtCol H. E. Allen, interv of 26 Feb 59. _General MacArthur Visits Marine Battalion_ Following the occupation of Hongchon on the 15th, the Marine ground forces ran into stiffening enemy opposition during the next two days. The 2d and 3d Battalions of the 7th Marines were pinned down by intense CCF mortar and artillery fire when attacking Hill 356 (Map 9). Three out of six friendly 81mm mortars were knocked out on 15 March in the 3d Battalion area, and at dusk 2/7 and 3/7 had barely won a foothold on the hill.[138] [138] CO 7thMar msg to CG 1stMarDiv, 2130 15 Mar 51. The 1st Marines also met opposition which indicated that the enemy planned to make a stand on the high ground east and north of Hongchon. An intricate maneuver was executed when Lieutenant Colonel Robert K. McClelland’s 2/1 swung from the right flank, where no enemy was encountered, to the extreme left. As a preliminary, the battalion had to circle to the rear, then move by truck up the MSR and through the zone of the 7th Marines as far as the village of Yangjimal (Map 9). Dismounting, the men made a difficult march across broken country toward Hill 246. At 1230 on the 15th the column deployed to attack Hill 428 in conjunction with Lieutenant Colonel Virgil W. Banning’s 3d Battalion.