Marine Helicopter Transport Squadron 161
15TMAW, c/o Fleet Post Office
San Francisco, California
10 Feb 1952
From: Commanding Officer, Marine Helicopter Transport Squadron 161
To: Commanding General, First Marine Division
Subj.: OPERATION MOUSETRAP
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:
That the operation would commence at 1030, 14 January 1952.
That approximately 1,180 troops would be airlifted from Camp Tripoli to DT 374-133 and
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:
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.
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.
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.
That an aircraft would reconnoitre the landing zone and select the most suitable
positions within it for landing sites.
That the improvement of these landing sites would be the responsibility of the
Commanding Officer, Air Delivery Platoon.
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.
That nine (9) aircraft would be assigned for the operation.
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.
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.
That ground crews from the Squadron would be present in the loading zone during the
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.
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:
That four (4) members of the Air Delivery Platoon would be assigned to the aircraft
making the reconnaissance of the landing zone.
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:
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.
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.
That the duties of the men at the loading sites would be as follows:
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:
That two (2) 800 gallon refuelers would be dispatched at 0900 from X-83 to Camp Tripoli.
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:
That two (2) pilots would be assigned to each aircraft.
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.
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).
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).
That aircraft would be refueled at Camp Tripoli and that the refueling sites were
located approximately 100 yards in front of the loading sites.
That five (5) aircraft would be assigned to the RED pattern and four (4) aircraft would
be assigned to the YELLOW pattern.
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.
That the maximum gross weight of the aircraft would be 6,900 pounds.
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.
That 425 pounds (71 gallons) of fuel would be carried in the rear tanks.
That aircraft would return to the loading site for refueling with a minimum of 75 pounds
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.
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.
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.
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.
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.
That an Operations Duty Officer would be assigned to the loading site to coordinate the
4. EXECUTION PHASE: (No. 1)
a. The operation commenced as
scheduled and was routine in every respect except for the following:
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.
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
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.
EXECUTION PHASE: (No. 2)
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.
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
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
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.
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.
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.
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
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.
OPERATION MOUSETRAP STATISTICS
14 January 1952
Number of Flights - 122
Number of Troops Carried - 638
First Aircraft Took-Off - 1000
Last Aircraft Landed - 1540
Total time to Complete the Operation - 5 hours 40 minutes
Total Flight Time - 41.5 hours
Total Fuel Consumed - 1,350 gallons
Average Refueling Time - 7 minutes
Number of Aircraft Participating - 9 - 2 hours 40 minutes; 8 - 45 minutes; 7 - 2 hours
16 January 1952
Number of Flights - 85
Number of Troop Carried - 442
First Aircraft Took-Off - 1145
Last Aircraft Landed - 1715
Total Time to Complete the Operation - 5 hours 30 minutes
Total Flight Time - 32.3 hours
Total Fuel Consumed - 1,400 gallons
Average Refueling Time - 7 minutes
Number of Aircraft Participating - 7 - 2 hours 40 minutes; 6 - 2 hours 50 minutes
17 January 1952
Number of Flights - 101
Number of Troops Carried - 511
First Aircraft Took-Off - 0720
Last Aircraft Landed - 1230
Total Time to Complete the Operation - 5 hours 10 minutes
Total Flight Time - 40.1 hours
Total Fuel Consumed - 1, 600 gallons
Average Refueling Time - 7 minutes
Number of Aircraft Participating - 10 - 2 hours 5 minutes; 9 - 3 hours 5 minutes