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1967, Marine, Navy, and corporate technicians and mechanics had replaced
the rear pylons on all but 16 of the 105 Sea Knight aircraft in the
Western Pacific. They refitted the remaining aircraft with the structural
modifications by February 1968.18

During the remaining months of 1968, the Marine Corps and Navy initiated the second phase during regularly scheduled maintenance overhaul of the 46s or those aircraft sent back because of extensive battle damage. Called Project Sigma, these modifications consisted of the installation of a new tail section, a new transmission mount, and a cruise guide indicating system.* While the second phase caused less of a drawdown of the CH-46 resources than the initial alterations, about 12 to 14 of the aircraft a month were either at Japan or Okinawa undergoing rework. In July, moreover, the 1st MAW reported two instances of the "structural failure of CH-46 rotor blades" manufactured prior to March 1967. This required the Marine Corps and Navy to undertake a new testing procedure of all the blades of that vintage. While this affected nearly half of the Sea Knights in the 1st MAW inventory, the wing accomplished most of the retesting in-country without impacting greatly on the tempo of operations.19**

While the Marine wing remained concerned about the continuing effectiveness
of the CH-46,*** several minor problems with replacement parts plagued
the large heavy-lift Sikorsky CH-53A Sea Stallion helicopter. General
Anderson, the wing commander, later observed that strictly because of
the lack of spare parts there were times in late 1967 and early 1968
when only three of the aircraft "would be available for flight." In
January 1968, HMH-463, the CH-53A squadron, averaged only a 31 percent
availability. During February, General McCutcheon in Washington raised
"such a fuss" in Navy aviation logistic cir-

* These modifications resulted "in added structural strength, and give the
pilot a means of monitoring the structural loads imposed on the airframe,
reducing the likelihood of overstress." Because of the magnitude of
these changes, they were accomplished as the aircraft underwent "Progressive
Aircraft Rework" (PAR) or Battle Damage Repair (BDR). There still remained,
however, significant differences about the extent of modifications needed
between the Boeing Vertol Corporation and the Marine Corps. For example
General McCutcheon in a letter to an official of the company insisted
that the Phase II modifications be carried out "in order to meet the
Marine Corps operational requirements." He also expressed his concerns
that a "desynch" device [to avoid intermeshing of the rotors] be added
to the list of modifications. While willing to soften his position to
the extent that he believed "it is "highly desirable' vice 'mandatory,'"
McCutcheon wrote "No matter how you look at it, the pilots still ask
the question, 'How do I get down safely if I have desynch and blade
intermeshing?'" The device was never added. McCutcheon to Robert W.
Tharrington, dtd 29Jan68, Ltr No. 28, File T, 1968 Cor, McCutcheon Papers;
FMFPac, MarOpsV, Dec68, p. 111.

** Another modification was added to the CH^i6s in 1968 that had nothing
to do with the structural problems. In February 1968, after much hesitation.
General Krulak, at FMFPac, finally approved an experiment of General
Anderson's, the wing commander, to replace the 7.62mm machine guns on
board the CH-46 with the .50-caliber guns. Major General McCutcheon
told Krulak after his visit to Vietnam in January 1968 that almost all
commanders, including a division commander, were in favor of the replacement
and willing to give up troop space to carry the heavier armament with
its greater range. According to McCutcheon, the question was which weapon
was "most effective in the air, not on the ground. . . . Perhaps if
you had a .50 to start with you might nor have been forced down." Faced
with the almost unanimous opinion from Vietnam, General Krulak relented.
He told both Generals Anderson and McCutcheon that while believing the
issue was "completely emotional . . . [but] I am no fool where emotion
is involved." With the final assent from FMFPac, General Anderson announced
that he desired to arm all of the 46s with the .50-caliber guns, but
would "leave it to the discretion of the group and squadron commanders,
however, as to whether or not they actually mounted the 7.62mm or the
.50-caliber." As General Anderson stared later, he did not want "to
make a dogmatic rule" but wanted to permit his commanders to determine
the best armament according to the particular circumstances. MajGen
Norman Anderson Itrs to McCutcheon, dtd 2 and 7Feb68, and McCutcheon
to Anderson, dtd 8Feb68, Letter No 50, File A and LtGen Victor H. Krulak
to McCutcheon, dtd 2Feb68 and McCutcheon Itr to Krulak, dtd 8Feb68,
Ltr No. 39, File K, 1968 Cor, McCutcheon Papers; MajGen Norman J. Anderson,
Comments on draft, n.d. IJan95] (Vietnam Comment File), hereafter Norman
Anderson Comments.

*** Besides the structural problems with the CH-46, Lieutenant Colonel
Roy J. Edwards, who commanded HMM-265 which operated with SLF Bravo
in the summer of 1968, related problems with fuel filters which were
unable to prevent the "super fine sand in this littoral region . . .
[from] being drawn into the fuel tanks as the helicopters . . . landed
on or near the beaches." After extended use, the sand "worked its way
into the fuel controls of the helicopter to prevent it from developing
full power." According to Edwards, "this [was] happening to all [emphasis
in the original] my helicopters even though they had all the routine
prescribed maintenance." He recalled two near-accidents caused by the
problem: "I had one a/c [aircraft] on a milk run take off from the carrier,
climbed straight ahead, lost power and sagged back on the carrier as
the carrier ran up under him! He was fully loaded with passengers, supplies,
and mail. Not one got their feet wet!" In the second incident, a helicopter
on the way to the beach from the carrier also lost power, "the pilot
kept the engine running and just flew into the water and taxied the
several miles to shore." Again there were no injuries nor damage. He
then halted flights of all of his CH-46s until the squadron could determine
a "fix". Eventually, they placed additional air filters on "the air
intake to the fuel tanks of the helicopter plus judicious monitoring/cleaning
of the fuel controls after each flight onto the beach where this 'superfine'
sand was being ingested. This didn't prevent the contamination but we
learned to live with it." According to Edwards, "it was a 'soul-searching'
experience to have to 'ground' my helicopters in the middle of a war,
while we found out . . . how to counteract." LtCol Roy J. Edwards, Comments
on draft, dtd 10Nov94 (Vietnam Comment File).

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