Marine Helicopter Transport Squadron 161
Operation Mousetrap Statistics

Declassified Document

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Marine Helicopter Transport Squadron 161
15TMAW, c/o Fleet Post Office
San Francisco, California

Ser 0147
10 Feb 1952

From: Commanding Officer, Marine Helicopter Transport Squadron 161
To:    Commanding General, First Marine Division


Ref:   (a) Map: AMS L-751 Korea, 1:50,000, Sections 6828 II, 6927 I, and 6927 IV

Encl:  (1) Statistics


To airlift two (2) companies of the 2nd Battalion, 5th Marines, from their Corps Reserve position at Camp Tripoli (DT 298-205) to positions in rugged mountainous terrain seven (7) miles to the South-East (DT 374-133 and 386-139).


a. To expedite the movement of these troops to positions from which they could rapidly deploy and form a tactical pattern designed to contain and capture an estimated 200 to 300 guerrillas.

b. To determine the feasibility of employing helicopters in anti-guerrilla operations and to develop tactics and techniques for such employment.


a. At 0100, 14 January 1952, a telephone call was received from the S-4, 5th Marines, who had been cleared by the Chief of Staff, First Marine Division, to effect direct liaison with HMR-161, and establish plans necessary for the movement of one (1) Battalion plus one (1) Company from Camp Tripoli to certain designated rear areas.  The following agreements were reached:

  1. That the operation would commence at 1030, 14 January 1952.

  2. That approximately 1,180 troops would be airlifted from Camp Tripoli to DT 374-133 and DT 386-139.

  3. That further liaison would be affected as soon as additional information became available and more complete plans formulated.

b. At 0730, 14 January 1952, liaison was again established between this squadron and the S-4, 5th Marines, and the following plan agreed upon:

  1. That the number of troops to be airlifted would be reduced from the original 1,180 to approximately 500, since the distance from Camp Tripoli to the desired tactical location was relatively short and trucks could transport the remaining troops to within a few miles of their destination.

  2. That two (2) loading sites and two (2) refueling sites would be established at Camp Tripoli by the 5th Marines; one (1) loading and one (1) refueling site would be outlined by RED panels, and the other loading and refueling site would be outlined with YELLOW panels.

  3. That the troops scheduled to be airlifted to DT 374-133 would load aboard the aircraft at the RED loading site, and the troops scheduled to be airlifted to DT 386-139 would load aboard the aircraft at the YELLOW loading site.

  4. That an aircraft would reconnoitre the landing zone and select the most suitable positions within it for landing sites.

  5. That the improvement of these landing sites would be the responsibility of the Commanding Officer, Air Delivery Platoon.

  6. That two (2) 800 gallon refuelers would be dispatched from X-83 to Camp Tripoli and that one (1) refueler would be assigned to each refueling site.

  7. That nine (9) aircraft would be assigned for the operation.

  8. That the normal payload for the aircraft would be five (5) combat equipped troops, or four (4) combat equipped troops plus equipment organic to the unit.  It was further decided that as gas was burned, an additional passenger or equipment would be added.

  9. That an officer from the Squadron would be assigned to the loading zone to coordinate the aircraft and to act in a liaison capacity between the Squadron and the 5th Marines.

  10. That ground crews from the Squadron would be present in the loading zone during the operation.

  11. That the FAC of the 2nd Battalion, 5th Marines, would provide communications at both the loading and landing zones on an assigned frequency of 142.02.  The call sign for the loading zone would be FAMILY 14, and the call sign for the landing zone would be WHOLESOME 14.

  12. That the operation would require approximately four (4) hours to complete.

c. After completing the above mentioned plans with the S-4, 5th Marines, the Commanding Officer, Air Delivery Platoon was contacted and the following decisions reached:

  1. That four (4) members of the Air Delivery Platoon would be assigned to the aircraft making the reconnaissance of the landing zone.

  2. That when two (2) landing sites were selected within the landing zone, two (2) members of the Platoon would be landed on each site to perform the following:

    (a) Effect improvements on the landing sites.

    (b) Mark the sites with the assigned panels.

    (c) Act as signalman for the aircraft during the operation.

    (d) Expedite the unloading of troops at the landing sites.

  3. That two (2) members of the Platoon would be assigned to each loading site at Camp Tripoli and that they would be passengers in the first two (2) aircraft departing from X-83 for Camp Tripoli at 1000.

  4. That the duties of the men at the loading sites would be as follows:

    (a) Direct aircraft in the approach to the loading site.

    (b) Expedite the loading of troops.

d. Upon completion of plans with the Commanding Officer, Air Delivery Platoon, the following decisions were made within the Squadron:

  1. That two (2) 800 gallon refuelers would be dispatched at 0900 from X-83 to Camp Tripoli.

  2. That an engineering crew of 20 men plus maintenance equipment would be assigned to the aircraft departing from X-83 to Camp Tripoli.  The duties of this crew would be to effect minor repairs and to refuel the aircraft.

e. Pilots were briefed at 0915 on the following points:

  1. That two (2) pilots would be assigned to each aircraft.

  2. That approximately 500 troops were to be airlifted from two (2) loading sites at Camp Tripoli to two (2) landing sites, one (1) at DT 374-133 and the other at DT 386-139.

  3. That one (1) loading site was designated RED and that all troops loaded at this site would be transported to the RED landing site (DT 374-133).

  4. That the other loading site was designated YELLOW and that all troops loaded at this site would be transported to the YELLOW landing site (DT 386 -139).

  5. That aircraft would be refueled at Camp Tripoli and that the refueling sites were located approximately 100 yards in front of the loading sites.

  6. That five (5) aircraft would be assigned to the RED pattern and four (4) aircraft would be assigned to the YELLOW pattern.

  7. That as gas was burned the pilot would signal to the Air Delivery man at the loading site to add an additional passenger or equipment.

  8. That the maximum gross weight of the aircraft would be 6,900 pounds.

  9. That the first aircraft in each pattern would refuel after completing two (2) round trips and the second aircraft in each pattern would refuel after completing three (3) round trips.  That the remaining aircraft would make as many trips as possible before refueling.

  10. That 425 pounds (71 gallons) of fuel would be carried in the rear tanks.

  11. That aircraft would return to the loading site for refueling with a minimum of 75 pounds of fuel.

  12. That the first aircraft would take off from X-83 at 1000 and proceed to Camp Tripoli with four (4) Air Delivery personnel, a crew chief, and first mechanic.  This aircraft would check on last minute details at the loading site.

  13. That the second aircraft would take off at 1015 and proceed to Camp Tripoli, land its passengers on the RED loading site, pick-up troops and proceed to the RED landing site.

  14. That the remaining aircraft committed to the operation would take off at one (1) minute intervals and proceed to Camp Tripoli, land their passengers, pick up troops at the assigned loading site and proceed to the corresponding landing site.

  15. That the route of approach and retirement would be governed by the terrain; aircraft would fly on the left hand side of valleys and in the event of an autorotation, a right turn would be effected to the floor of the valley.

  16. That the assigned frequency for the operation was 142.02, Channel RED, and the call sign at the landing site would be FAMILY 14.  The call sign at the landing site would be WHOLESOME 14.

  17. That an Operations Duty Officer would be assigned to the loading site to coordinate the operation.


a. The operation commenced as scheduled and was routine in every respect except for the following:

  1. One (1) aircraft was downed because of mechanical failure and another aircraft was dispatched to X-83 to obtain the necessary parts to effect the repair.  This aircraft was detained at X-83 due to mechanical difficulty of its own, but eventually returned to the loading zone with the needed parts.  Because of these mechanical difficulties the services of these two (2) aircraft were lost for a period of approximately two (2) hours.

  2. As the operation reached its final stage, a request was made by the X-4, 5th Marines, to airlift an additional 86 men from Camp Tripoli to the following locations:

    (a) DT 365-164

    (b) DT 416-103

    (c) DT 385-106

    (d) DT 372-108

  3. These troops were assigned to designated landing sites and as aircraft landed to pick them up, the pilots were given the coordinates of their destinations.

b. The lift was completed at 1540.


a. On 15 January, at the request of the S-3, 5th Marines, five (5) helicopters were flown to the 2nd Battalion, 5th Marines C.P. located at DT 380-130.  These aircraft were requested to support, in conjunction with the guerrilla mop-up operations, the troops airlifted to this area on the previous day.  Upon reporting at 0730 it was decided that two (2) aircraft would be sufficient to handle the utility assignments requested and three (3) aircraft were returned to X-83.  A relief system for the two (2) remaining aircraft was established whereby two (2) helicopters with crews reported to the C.P. at two (2) hour intervals throughout the day.

The two (2) aircraft that remained at the C.P. were employed by the Commanding Officer of the Battalion to reconnoitre his positions, to regain contact with elements that had no radio contact, to make supply runs between the Battalion dump and the C.P., to evacuate casualties from the C.P. to Camp Tripoli, to pick-up prisoners taken in the guerrilla operation and to return them from the Company C.P.'s to the Battalion C.P., carry prisoners from the Battalion C.P. to Camp Tripoli, and to lift certain critically needed equipment from the Battalion C.P. to positions on the line.  In most cases it was not possible to land the helicopters when supplying units on the line because the ridge positions occupied by troops were too uneven and were generally too densely forested to permit landings.  Supplies were lowed by rope while the helicopters hovered over troop positions.  In most instances this involved hovering out of ground effect at an altitude of 3,000 to 4,000 feet and was only made possible by the fact that there was a wind of approximately 20 knots.

The following day at 1130 an airlift was commenced to return the entire Battalion to Camp Tripoli.  Two (2) loading sites were selected and marked by panels in the vicinity of DT 408-137 and two (2) landing sites that had been used for the previous days operation were established at Camp Tripoli.  After all personnel had been lifted from these sites, aircraft were diverted by the FAC to two (2) loading sites at the Battalion C.P. where the remaining troops were located.  The operation continued until 1700 and approximately 462 troops were returned to Camp Tripoli.  The operation was commenced again at 0730 on 17 January lifting the remaining troops from the Battalion C.P. to Camp Tripoli and was completed at 1230.


a. A unique aspect of this operation was the unusually brief planning stage.  The first word of the operation was received at 0100, 14 January 1952, and take-off time was established at 1000 the same day, therefore, most of the liaison between the 5th Marines and this squadron was accomplished over the telephone.  It was not possible to establish the close personal liaison essential for finely polishing the plans of the operation and in addition there was a limited time available to select and prepare the sites where the troops were to be landed.  A thorough reconnaissance of the objective area could not be made and landing sites had to be chosen hastily.

b. Prior to the initial take off the time interval between aircraft in each traffic pattern was set at one minute; however, since the distance between the loading and landing zone was approximately seven (7) miles and only four (4) or five (5) aircraft were in each circle, it soon became apparent that the pilots could take adequate interval by visual means alone.  In addition, aircraft downed for refueling or mechanical adjustments made the time factor less important in maintaining a safe interval between aircraft.  At one time, for example, there might only be two (2) aircraft flying in the pattern between the YELLOW sites; therefore, in the interest of expediting the operation, aircraft were allowed to depart from the loading zone with little regard for interval.

c. Relatively congested conditions at the loading zone introduced an element of danger not heretofore encountered in this squadron's airlift operations.  It was necessary for the airlift to make most approaches and departures from the loading zone over tents and congested areas bordering the field.  Wires at both ends of the field, a 50 foot flag pole at one site, and at times several aircraft in various stages of approach and departure, required alert flying and extreme caution.

d. Three (3) spare pilots were flown from X-83 to Camp Tripoli when the operation began.  When aircraft were landed for refueling, one of the spare pilots would be designed to replace one of the incoming pilots and the relieved pilot would then standby for re-assignment.  In this manner, pilots were rotated and given an opportunity to take a brief rest.

e. The troop landings made in the vicinity of DT 385-106 were interesting; these zones had not been previously reconnoitered and no prepared landing sites existed. Two of the landing zones were located in such a position that little or no wind could be counted upon for additional lift and since the aircraft were operating at a gross weight of approximately 6,900 pounds at an altitude of 2,500 to 3,000 feet, sufficient forward speed had to be maintained to insure adequate lift until the aircraft was over the intended landing spot.  Landing conditions were further made difficult by the fact that the ground was snow covered which made obstacles difficult or impossible to detect.  Once committed to the landing, there was no alternate maneuver.


a. OPERATION MOUSETRAP illustrated that a relatively large number of troops can be moved by helicopter on very short notice.  Experiences gained from similar problems proved invaluable in this operation.  With a minimum of planning and briefing, necessitated by the lack of time, the entire operation was completed with only minor difficulties.

b. This operation demonstrated the desirability of refueling, either at the loading zone, or between the loading zone and the landing zone.  Much time was saved by the fact that it was unnecessary for aircraft to return to X-83 to refuel.

c. The employment of helicopters in anti-guerrilla operations is highly feasible.  However, plans for their use should be more closely integrated with the ground troops scheme of maneuver.

d. It is believed that following the airlift much of the utility work performed during the guerrilla operation could have been more economically and efficiently accomplished by the use of the HTL type helicopter.

e. The helicopters could have been more effectively utilized had ground personnel and particularly the FAC been more fully aware of the capabilities and limitations of the aircraft.

f. Special attention should be given to the thorough indoctrination of FAC's in transport helicopter operations.

g. FAC's should be utilized more extensively in the planning as well as the execution stage of all airlifts.  They should screen all requests for helicopters and assign each approved request a priority.

h. Communications with and identification of troop elements was not positive during this operation and some means of air-ground communications and identification must be established.  Colored panels could be used to mark company positions or the positions of separate patrols, colored smoke grenades could also be used for this purpose.  Mirrors could be issued to individuals for signaling purposes and a definite panel pattern or colored smoke combinations could be used to mark casualty pick-up sites.  Portable electric (bull horn) speakers could have been very useful in establishing one-day communications with the ground elements from the airborne helicopters.

i. Padded drop bags similar to those used by the 1st Air Delivery Platoon could have been utilized to drop critically needed supplies to units located in terrain unsuitable for landing or hovering.

j. Patrols and small troop elements should be airlifted and landed in mass.  On this operation, individual patrols at times experienced difficulty in assembling because the aircraft were dispatched singulary and sometimes landed 200 to 300 meters apart.  Because of rough terrain and the additional handicap of fairly deep snow, the rapid organization of personnel essential in this type of operation was delayed.

k. Predesignated supply points might be useful in the support of patrol operations and helicopters would be used to stockpile supplies at them.  If this system is feasible from an infantry commander's viewpoint, locating and identifying patrols by helicopter would be simplified.


a. That the closest liaison possible exist between the ground unit and the helicopter squadron and the helicopter commander be informed of the ground troop commander's scheme of maneuver.

b. That the HTL type helicopter be more fully utilized in utility work and the transport type helicopter be employed only when the HTL is unable to perform this mission.

c. That all FAC's be thoroughly schooled in the capabilities and limitations of helicopters and that this program be conducted by HMR-161 and coordinated by the Division Air Office.

 d. That a study be made of an air-ground communications system so that the helicopters can communicate with units down to the squad level.

e. That a suitable portable electric bull horn be manufactured and included in the T/E of all helicopter squadrons.

f. That patrols in an operation of this nature be equipped with colored panels and colored smoke grenades.

g. That patrols or small troop elements be airlifted and landed in mass.

K.B. McCutcheon


14 January 1952

  1. Number of Flights - 122

  2. Number of Troops Carried - 638

  3. First Aircraft Took-Off - 1000

  4. Last Aircraft Landed - 1540

  5. Total time to Complete the Operation - 5 hours 40 minutes

  6. Total Flight Time - 41.5 hours

  7. Total Fuel Consumed - 1,350 gallons

  8. Average Refueling Time - 7 minutes

  9. Number of Aircraft Participating - 9 - 2 hours 40 minutes; 8 - 45 minutes; 7 - 2 hours 15 minutes

16 January 1952

  1. Number of Flights - 85

  2. Number of Troop Carried - 442

  3. First Aircraft Took-Off - 1145

  4. Last Aircraft Landed - 1715

  5. Total Time to Complete the Operation - 5 hours 30 minutes

  6. Total Flight Time - 32.3 hours

  7. Total Fuel Consumed - 1,400 gallons

  8. Average Refueling Time - 7 minutes

  9. Number of Aircraft Participating - 7 - 2 hours 40 minutes; 6 - 2 hours 50 minutes

17 January 1952

  1. Number of Flights - 101

  2. Number of Troops Carried - 511

  3. First Aircraft Took-Off - 0720

  4. Last Aircraft Landed - 1230

  5. Total Time to Complete the Operation - 5 hours 10 minutes

  6. Total Flight Time - 40.1 hours

  7. Total Fuel Consumed - 1, 600 gallons

  8. Average Refueling Time - 7 minutes

  9. Number of Aircraft Participating - 10 - 2 hours 5 minutes; 9 - 3 hours 5 minutes



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