A unique rescue and recovery operation also came into existence about this time. On 19 April the division ordered the 5th Marines, occupying the center regimental sector, to organize a tank-infantry force for rescue of the United Nations Truce Team, should such action become necessary. The regimental plan, published on 22 April, utilized a reinforced rifle company-tank company organization directly supported by organic 5th Marines 4.2-inch mortars and 1/11. The Everready Rescue Force, from the regimental reserve, occupied the high ground (OP 2) east of and dominating Panmunjom.
In addition to setting forth organizational details of the task unit, the 5th Marines Operational Plan 6-52 specified the method of operation for the rescue force. Taking advantage of the peace corridor in the western end of the center sector, a Forward Covering Force would speed tank-riding infantry to the high ground one-half mile beyond the objective, Panmunjon. Following would be the Pick-Up Force, from the 1st Tank Battalion Headquarters Platoon, which would retrieve the principal UN delegates and take them quickly to the assembly area two miles to the rear of the MLR. A Rear Covering Force, composed of a tank-infantry element, would follow the Pick-Up force both on its way towards the objective and on the return trip. Withdrawal of both covering forces was regulated by a series of phase lines.
Marine Air Operations[52]
[52] Unless otherwise noted, the material in this section is derived from: PacFlt EvalRpt No. 4, Chaps. 9, 10; 1st MAW, HMR-161, VMO-6 ComdDs, Apr 52; Lynn Montross, Cavalry of the Sky—The Story of U. S. Marine Combat Helicopters (New York: Harper & Brothers, 1954), hereafter Montross, SkyCav, quoted with permission of the publishers.
Even though the Marine air-ground team had been shorn of much of its tactical aviation, what remained was well utilized. Helicopter troop operations had become commonplace by the end of April 1952. That month there were three exercises to further evaluate tactical concepts of helicopter employment. Operation PRONTO, conducted on 5 April, was the first major troop lift in the new I Corps sector. In this maneuver approximately 670 troops of 2/7 and 10,000 pounds of rations were transported by helicopter and truck from the Munsan-ni vicinity across the Han River to the Kimpo Peninsula. Here the reserve battalion served as a counterattack force in a hypothetical enemy landing. Due to the necessity for avoiding the neutrality zone in the Munsan area, round-trip flights averaged about 57 miles.
The exercise combined the shortest notice and longest distance of any large-scale helicopter troop movement conducted by HMR-161. It pointed to the fact that a helicopter unit could successfully lift a troop organization virtually as an “on call” tactical tool and without the benefit of previous liaison.
Operation LEAPFROG, on 18–19 April, transported one KMC battalion across the Han to the peninsula and lifted out another the following day. The purpose of this test was to determine the feasibility of a replacement movement conducted over water, with “consideration given to the language barrier existing between the troops and the transporting facility.”[53] The six-mile round trip was the shortest troop haul yet made by the transport chopper squadron. Consequently, it took the 12 HRS-1 single-engine Sikorsky aircraft only 3 hours and 26 minutes to complete the exchange of the 1,702 KMC troops.
[53] PacFlt EvalRpt No. 4, 10-73.
Colonel McCutcheon’s HMR-161 pilots found that their helicopters could carry six combat-equipped Korean Marines instead of five American Marines, due to the smaller size and weight of the average Korean. Since the U.S. and KMC Marine battalions were the same size, the larger load factor for the Korean Marines enabled their unit to be moved faster. In LEAPFROG the language difference proved to be no handicap, since there were sufficient interpreters on hand and the troops were cooperative. Helicopter pilots could use landing sites close together because the terrain was open and the area of operations beyond the reach of Chinese artillery.
Close on the heels of LEAPFROG came a third airlift. Operation CIRCUS, conducted on 23 April, provided for the air deployment of the 7th Marines reserve regiment, minus two battalions, across the Imjin to landing sites just to the rear of the secondary defensive line, WYOMING FORWARD. Ten helicopters carried 1,185 Marines over the river barrier to blocking positions in 90 minutes. The CIRCUS exercise illustrated that a minimum distance should be maintained between loading and unloading sites for a safe and efficient transport operation. It also pointed up that “consideration must be given to the number of aircraft assigned to each traffic pattern during short hops over a river.”[54] This successful maneuver came three days before all HRS-1 aircraft were grounded due to a defect in the tail rotors. By mid-May the problem had been corrected and the aircraft returned to flying status.