INTELLIGENCE MEMORANDUM NORTH VIETNAMESE SEA INFILTRATION OF MILITARY SUPPLIES INTO SOUTH VIETNAM

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP85T00875R001700020009-9
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 16
• Document Creation Date: December 22, 2016
• Document Release Date: April 12, 2010
• Sequence Number: 9
• Publication Date: August 1, 1971
• Content Type: IM

Sanitized Copy Approved for
Release 2010/04/12 :
CIA-RDP85T00875R0017000
Sanitized Copy Approved for
Release 2010/04/12
oaTnno7amnnol7000 Completed
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
ealmx
Secret
DIRECTORATE OF
INTELLIGENCE
Intelligence Memorandum
North Vietnamese Sea Infiltration of Military Supplies
Into South Vietnam
Secret
ER IM 71-156
August 1971
Copy No. 64
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
WARNING
'T'his document contains information affecting tic national
defense of the United States, within the meaning of Title
18, sections 793 and 794, of the US Code, as amended.
Its transmission or revelation of its contents to or re-
ceipt by an unauthorized person is prohibited by law.
GROUP 1
I teclud,d from nuiomadc
L downgrodfmr and
dcrl ,"if,corinn
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
CENTRAL INTELLIGENCE AGENCY
Directorate of Intelligence
August 1971
NORTH VIETNAMESE SEA INFILTRATION
OF MILITARY SUPPLIES INTO SOUTH VIETNAM
Conclusions
1. Since closure of the Sihanoukville supply corridor in January
1970, the North Vietnamese have expanded their logistical system in
southern Laos and northeast Cambodia. However, we have not yet detected
a capability on their part to move large quantities of supplies from the
Cambodian provinces of Kompong Cham and Kratie (at the lower end of
the system) farther south into South Vietnamese Military Region (MR) 4.
This shortcoming may explain the increased efforts over the past 18 months
on the part of the Communists to infiltrate supplies by sea. Over the past
two years, there has been a total of 20 attempts detected - more than
the total such attempts during the 1965-68 period - and MR 4 has been
the destination of all the trawlers for which terminal destination could be
estimated.
2. During 1970-71, the Communists managed to make two
infiltrations by sea, the only known successes since 1964. Despite these
two penetrations - which were not sufficient to meet enemy supply
requirements in MR 4 - Market Time's record in blocking sea infiltration
has been excellent.
3. With the replacement of its P-3 aircraft by land-based radar
surveillance, however, the effectiveness of Market Time against trawler
infiltration probably will decline and enemy infiltration attempts almost
certainly will increase. Consequently seaborne infiltration may come to
assume an important supply role, in the Delta and the regular resupply
of Communist forces in MR 4.
Note: This memorandum was prepared by the Office of Economic Research
and coordinated within CIA.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
Discussion
4. During the past two years there has been a sharp increase in
attempts by North Vietnam to infiltrate supplies by sea into South Vietnam.
This memorandum reviews the history of this logistical practice and assesses
its importance in relation to the supply requirements of the enemy's forces
in South Vietnam. The memorandum also briefly examines the present and
projected capability of Market Time, the Allied naval program designed to
neutralize such infiltration attempts.
Background
5. In addition to the Ho Chi Minh Trail through Laos and the
Sihanoukville corridor through Cambodia, North Vietnam has made use of
seaborne infiltration of supplies by steel-hulled trawlers -1/ to provide
support to its forces in South Vietnam. A Viet Cong captured in 1965
stated that between 1960 and 1964 North Vietnamese trawlers infiltrated
material into South Vietnam on 20 occasions. Documents captured in the
same year indicated that from January 1964 to January 1965 as many
as two trawlers per month delivered cargo to Communist forces in MR 4.
Although the magnitude of the enemy's s;.-- infiltration efforts into other
military regions prior to 1965 cannot be accurately determined, there is
little doubt that the Communists were meeting a substantial amount of
their countrywide external requirements by trawler infiltration. Communist
use of this mode of resupply was interrupted in February 1965, however,
when an enemy trawler was destroyed ,it Vung Ro Bay in GVN MR 2.
Market Time Interdiction
March 1965 - August 1969
6. The month following the sinking of the North Vietnamese trawler
in February 1965, the US Navy initiated its Market Time sea indiction
program along the coast of South Vietnam. In the subsequent three-year
period through March 1968 the enemy was detected attempting to infiltrate
supplies into South Vietnam by trawler on 12 different occasions, or an
average of only once every three months. 2/ (No infiltration trawlers were
1. Hereafter simply called trawlers.
2. Detected infiltration attempts by trawlers are shown in Appendix A.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
detected between March 1968 and August 1969.) During the period March
1965 - March 1968 eight trawlers were destroyed and four forced to abort
their attempts at infiltration.
7. During the March 1965 - March 1968 period, trawlers were
detected in attempts to infiltrate materiel into coastal areas of MRs 1, 2,
and 4. These attempts probably were made to meet specific short-term local
needs, however, rather than representing an attempt at routine resupply.
Moreover, at least in 1968, sea infiltration attempts were crisis oriented.
Trawler crews appeared to be reluctant to abort their missions; they tried
to outmaneuver and outgun larger and faster Allied craft and were
destroyed. Also illustrating the crisis-oriented character of the 1968
attempts, in February five attempts were made, four within 48 hours. These
attempts occurred shortly after the heaviest fighting of the Tet offensive
of 1968 when enemy stocks probably were at low levels. At no other time
during the war were enemy sea infiltration attempts closely correlated with
enemy offensive activity in South Vietnam. In this connection, however,
a strong correlation between infiltration attempts and weather conditions
was noted during the March 1965 - March 1968 period. Ten of the
12 trawlers detected were attempting to infiltrate during the northeast
monsoon (November-April) a time when Allied surveillance capabilities
in northern and central South Vietnamese coastal waters are inhibited by
poor visibility and heavy sea conditions.
August 1969 to the Present
8. Discovery of an enemy trawler in late August 1969 off the coast
of MR 4 ended an 18-month standdown in detected Communist sea
infiltration attempts. Since this resumption there has been a total of 20
attempts detected, of which 16 aborted, two were destroyed, and two
successfully infiltrated supplies. Events in Cambodia clearly precipitated this
rash of attempts. In May 1969, Sihanouk embargoed arms shipments to
VC/NVA base areas; he subsequently lifted the ban in September 1969,
but shipments were halted permanently on 10 January 1970. His
subsequent ouster and the Allied incursions into Communist base areas in
Cambodia during the spring of 1970 ended any enemy hope that the
Sihanoukville corridor would be reopened and forced the Communists to
look for alternative means of supplying combat forces in southern South
Vietnam.
9. To take up this slack, the North Vietnamese expanded the Ho
Chi Minh Trail through Laos into Cambodia during the 1970-71 dry season.
Currently, it is capable of supporting enemy forces in northern and central
South Vietnam as well as east-central Cambodia. At present, however, the
enemy does not possess the logistical capability in place to move large
SF.C:R F.T
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
quantities of materiel from base areas in the Cambodian provinces of
Kompong Chain and Kratie - which receive supplies from Laos - into
southern Cambodia and GVN MR 4. Thus he has had to place greater
reliance on seaborne infiltration into this area. This shift in emphasis to
MR 4 and the expansion of the sea infiltration effort is supported by ample
evidence. Since August 1969, the enemy has averaged about one attempt
per month, and MR 4 has been the destination of all the trawlers for which
a terminal area could be estimated. (See the map for known current
infiltration corridors.)
10. During the post-August 1969 period the North Vietnamese also
altered their standard operating procedures: trawlers once detected and
aware of Allied surveillance no longer attempted further penetration but
aborted their missions. Four-fifths of the trawlers detected aborted their
missions and returned safely to Communist waters. Two trawlers, destroyed
during the period, J probably were unaware of the surveillance and were
sunk shortly after entering South Vietnamese territorial waters off the coast
of MR. 4. Unlike the 1965-68 period, the pattern of infiltration missions
undertaken since August 1969 has had no apparent correlation with
prevailing weather conditions.
11. The North Vietnamese are known to have successfully penetrated
the Market Time barrier only twice since the program was initiated, both
occurring since August 1969. In August 1970 an SL-4 trawler (see the
photograph) evaded Allied surveillance and infiltrated munitions into An
Xuyen Province of MR 4. J In March 1971 an SL-6 trawler (see the
photograph) was discovered in a canal at the tip of the Ca Mau Peninsula,
also MR 4. The craft, estimated by the US Navy to have been in place
less than four months, had apparently become mechanically disabled and
when found was stripped and abandoned. It is possible, of course, that
some trawlers successfully delivered cargo and returned to North Vietnam
undetected by Market Time. A recent rallier from MR 4 has stated that
a trawler successfully infiltrated supplies into Kien Hoa Province in early
1970. Another source stated that a trawler successfully delivered supplies
to GVN MR 2 in 1971. These reports, however, have not been
substantiated.
12. A new type of infiltration craft - the SL-8 - added to the North
Vietnamese trawler inventory in mid-1970 brings a new dimension to the
problem (see the photograph). The SL-8 has a capacity of about 400 tons
3. A listing of cargo salvaged from a trawler destroyed in November 1970
appears in Appendix B.
4. Appendix C provides information on the types and characteristics of
trawlers in the Communist inventory.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
Infiltration of Enemy Military Supplies into South Vietnam
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
compared with capacities of about 100 tons for most of the other trawlers.
The SL-8`s seagoing capabilities are estimated to permit op,.--m ocean
operations in any weather short of typhoon conditions. In fact, the SL-8
is considered capable of navigation through turbulent coastal waters to
sheltered anchorages in sea conditions which would preclude the operation
of the vast majority of Market Time surface craft. In the three months
February-April 1971, three SL-8s were used on infiltration missions: two
aborted and one was destroyed.
Market Time: Process and Performance
13. Market Time employs aircraft and surface ships in three barriers
along the South Vietnam coast. The outermost barrier (50 to over 200 miles
from the coast) is maintained by P-3 aircraft operating under US Navy
control (see the photo,graph). These patrol craft conduct daily surveillance
operations over the areas indicated in the map. The patterns flown roughly
parallel large segments of inboun,l trawler tracks thus affording air crews
maximum opportunities to detect infiltration trawlers (see the map). 5/
This air barrier has been extremely effective in detecting enemy trawlers
and is the mainstay of the present Market Time operation: all but one
of the trawlers detected by Market Time forces since August 1969 were
initially sighted by P-3 crews.
14. Although the air barrier is highly effective in locating enemy
trawlers, it is defensive and does not necessarily result in the destruction
of an infiltrator. During overt surveillance, continuous visual and radar
contact with the trawler is attempted and the trawler is usually aware of
the surveillance. Once aware of airborne surve+:iiance, the infiltrator aborts
his mission while in international waters and returns to Communist ports.
Through this cautionary tactic the enemy is able to probe the barrier,
maximizing opportunities for successful penetration without incurring major
losses. To counter this tactic, Market Time forces have employed covert
surveillance tactics in order to lure the trawler into South Vietnamese
territorial waters where it can be destroyed or captured. Covert surveillance
relies upon an initial sighting and identification by the aircraft, which then
leaves the area and is relieved by another aircraft or by surface ship.. The
trawler may take evasive action in an attempt to ascertain whether or not
it has been spotted. If convinced that no surveillance is being maintained,
the trawler continues to fulfill its assigned mission. When the trawler enters
South Vietnamese territorial waters it is brought under fire. Since
mid-November 1970, of the five infiltration attempts detected by Market
5. Additional flight patterns have been designed and have been employed
in high threat areas.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
Time forces, covert surveillance was maintained in two instances, and in
both cases the trawlers were destroyed.
15. The surface barriers have a significantly lower rate of effectiveness
than the outer air barrier. The outer surface barrier is maintained by both
US Navy and Vietnamese Navy ships including two destroyer escorts, two
Coast Guard cutters, and several smaller ships. These craft conduct surface
surveillance of detected infiltrators and engage trawlers once they have
entered South Vietnamese territorial waters. The ships patrol areas
approximately 12 miles off the coast of South Vietnam. The inner surface
barrier is manned by numerous craft and is under complete control of the
South Vietnamese Navy. They have little effectiveness against any infiltrating
trawlers which may evade the air and outer surface barriers. Inner surface
barrier ships are employed primarily against enemy coastal transshipment
activity along the South Vietnamese coast.
16. A new coastal radar surveillance system is being constructed which
is intended eventually to replace US aircraft on the outer air barrier. The
system will comprise 16 sites and is scheduled to be operational by early
1972. This system almost certainly will not be nearly as effective a deterrent
as the air barrier: reaction and surveillance time will decrease from a few
days to only two or three hours.
Future Prospects for Sea Infiltration
17. Currently, North Vietnam has 23 trawlers in the six classes it
has used for infiltration attempts which, barring Allied interdiction, could
deliver more than 5,000 tons per month into South Vietnam - a capacity
sufficient to fulfill the Communist munitions requirements for all of South
Vietnam for an entire year at current consumption rates. Because of Market
Time, however, the enemy probably is not capable of meeting even current
needs in MR 4 by trawler deliveries. Estimated enemy weapons and
ammunition requirements in MR 4 during 1970 were between one and two
tons per day. The total estimated capacity of the two trawlers known to
have successfully evaded Market Time that year was about 200 tons --
roughly half the lower range of our estimate of the Communist annual
external supply requirements for the region.
18. It seems likely that the enemy intends to develop the seaborne
infiltration system for 'resupplying some of its forces in southern South
Vietnam. A Viet Cong rallier reported that in July 1970 COSVN planned
to establish alternate supply routes into the Delta area of South Vietnam.
He stated that because COSVN had written off Sihanoukville as a supply
source and because it believed MR 4 would be difficult to supply via the
Ho Chi Minh Trail, it had reactivated Rear Services Group 962 which,
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
before becoming inactive in December 1966 - when munitions began
arriving at Sihanoukville - had been responsible for the receipt, distribution,
and storage (of munitions sent by sea from North Vietnam to MR 4. Also,
documents recovered in Kien Hoa Province, in December 1970, revealed
that personnel of the 126th Naval Sapper Regiment had been sent by the
North Vietnamese Naval High Command to reconnoiter streams and canals
in MR 4 as feasible off-loading points for cargoes delivered by sea. Some
of these personnel are believed to have been aboard the trawler destroyed
off the coast of Kien Hoa Province in November 1970.
19. Geographically, MR 4 with its many canals and rivers is well suited
for seaborne infiltration. Waterways provide a natural cover which inhibit
Allied detection and afford the Communists access to base areas throughout
the region. Countless fishing junks and sampans further frustrate Allied
efforts to eliminate enemy resupply traffic. Although the South Vietnamese
have made considerable progress in recent years in securing areas of MR 4,
in the key provinces of Kien Hoa and An Xuyen - considered likely
terminal areas for seaborne infiltration attempts - the Communist
infrastructure continues to control significant portions of the population.
20. Market Time's ability to thwart this threat will be significantly
impaired when US naval forces are withdrawn and the air barrier is replaced
by the Vietnamese-operated coastal radar surveillance system. Efforts
currently are being made by South Vietnamese army and navy forces to
secure the high threat coastal areas of MR 4. If successful, this would deny
enemy access to trawler off-loading sites and offset to some extent the
probable future deterioration in Market Time's performance.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
APPENDIX A
Detected North Vietnamese Seaborne Infiltration Attempts
by Steel-Hulled Trawler Since the Initiation of Market Time Operations
Mar-Dec
1965
Number of Detection
Detections Date Result
10 May Destroyed
19 Jun Destroyed
23 Dec Aborted
1 Jan Destroyed
14 Mar Destroyed
11 Jul Destroyed
22 Feb Aborted
28 Feb Destroyed
29 Feb Destroyed
29 Feb Aborted
29 Feb Destroyed
24 Aug Aborted
16 Nov Aborted
23 Dec Aborted
11 Mar Aborted
21 Apr Aborted
19 May Aborted
29 May Aborted
10 Jun Aborted
6 Jul Aborted
2 Aug Aborted
28 Aug Successful
4 Sep Aborted
9 Oct Aborted
28 Oct Aborted
19 Nov Destroyed
Late Dec Successful
1970-Mar
1971 a/
24 Feb Aborted
22 Mar Aborted
27 Mar Aborted
8 Apr Destroyed
Destination
by Military
Region
4
4
4(Est.
Unknown
4
4
Unknown
4
4
Unknown
4
4
a. An SL-6 trawler was discovered disabled in southern An
Xuyen Province in March 1971. The trawler probably infil-
trated South Vietnam between late December 1970 and March
1971. This infiltration is thus counted in the 1971 total.
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
APPENDIX B
Major Items-recovered from SL-3 Trawler
Sunk Off Kien Hoa Province
on November 1970
Weapons
195 AK-47 rifles
7.62-pistol
50 B-40 rocket launchers
48 B-41 rocket launchers
6 75-mm recoilless rifles
Ammunition
754 Cases and 31 boxes of 7.62 ammunition
424 B-40 rocket rounds
466 B-41 rocket rounds
95 107-mm rocket rounds
242 75-mm recoilless rifle rounds
Miscellaneous
134 boxes of TNT (30 pounds per box)
30 boxes of TNT (65 pounds per box)
24 boxes of batteries (four per box)
49 boxes of C-3 plastic explosives
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
 Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9
SECRET
APPENDIX C
North Vietnamese Inventory of Infiltration Trawlers
Type
Inventory
(Units)
Beam
(Faet)
Length
(Feet)
Speed
(Knots)
Capacity
(Metric Tons)
SL-1 f
33
20
125
12-15
200
SL-2
6
19
125
17-over 25
150-200
SL-3
2
18
88
14
100
SL-4
5
19
99
14
100
SL-5
1
22
110
14
100
SL7-6 b/
Unknown
18
96
14
100
SL-7 of
4
18
110
Over 25
150-200
SL-8
9
27
150
15
400
Wu Hu a/
7
18
81
Unknown
75
a. The SL-1, SL-7, and the Wu Hu have not been observed
attempting to infiltrate cargoes to South Vietnam, although
they could be used for this purpose.
b. Photography of 18 June 1971 indicates that the Communists
may have replaced the one previously identified SL-6 which
was discovered abandoned in the Delta in March 1971 (see
paragraph 11).
SECRET
Sanitized Copy Approved for Release 2010/04/12 : CIA-RDP85T00875R001700020009-9