273. Memorandum From the President’s Special Assistant (Rostow) to President Johnson1

Mr. President:

Herewith a CIA paper I asked to be prepared on North Vietnamese losses during infiltration.

They calculate that:

  • —losses increased from 1965 to 1966;
  • —losses averaged 20% in 1966;
  • —although sickness and defection were the major direct causes, bombing had a big indirect effect by lengthening routes, increasing time en route, etc.
  • —in my notes on Senator Mansfield I said: “Several prisoners report that bombing results in the loss of more than half those whom they try to infiltrate.”

Although I would now use the average CIA figure, here are some of the reports which underlay that sentence:

North Vietnamese soldier detained on June 16, 1967, stated that of group of 300 men infiltrating, there were only 30 on arrival.
Desertion rate of North Vietnamese coming into Laos mounting daily, had reached 40% as compared to 5% in past years; but figure as high as 80% for Montagnards recruited into North Vietnamese forces.
A member of the 324th Division reported that 15 men out of his 170-man group deserted; another soldier reported that 26 out of his 52-man group deserted.

[Page 679]

Without bombing of infiltration trails—with all their direct and indirect effects—these desertions, disease rates, etc., would not be occurring.

Moreover, if we weren’t bombing, the total level of attempted infiltration would be much, much higher than it is.

With the greatest possible respect, I don’t back away from my difference with Bob McNamara on this.



Intelligence Memorandum



The limited evidence available for 1966 indicates that a substantial number—perhaps as many as 20 percent—of the North Vietnamese who began infiltration to South Vietnam through Laos were lost en route. The total number lost was nearly 10,000 men if the 53,000 accepted total of infiltrators is used as a base or about 15,000 men if the 81,000 total of accepted and possible infiltrators is used. The loss rate for those who came through the Demilitarized Zone appears to have been somewhat lower, probably because of the lower incidence of illness during the shorter journey.

Evidence for 1967 is still too limited to permit comparison. It is clear, however, that en route losses during infiltration are continuing at a significant rate. As further information becomes available it should be possible to be more certain both of the total loss figure during infiltration and the percentages lost through various causes.

The 1996 Infiltration Losses and Their Causes

Three fourths of the losses of infiltrators via Laos in 1966 resulted from death or permanent incapacitation because of illness, mainly malaria. About 10 percent were killed by air attacks and 5 percent were permanently lost through desertion.

The 1966 loss rate appears to have increased several times over the 1965 rate. Evidence on losses in 1965 is very limited. There appears, however, to have been an increased incidence of serious sickness in [Page 680] 1966. In addition, available reports for 1965 attributed no losses directly to air strikes although undoubtedly some infiltrators were killed or seriously wounded in this manner.

Perhaps as many as half of all infiltrating troops suffer to some degree from malaria en route to South Vietnam. As a result of malaria and other health problems, it is possible that nearly 20 percent of those who arrive in the South are not immediately fit for combat. Most of these men, however, probably recover sufficiently for combat.

Although air strikes apparently do not directly cause many casualties, they have had other significant effects on the loss rate. One of the most important has been to force infiltrating units to change their mode of movement in North Vietnam from truck to travel on foot, thus increasing the time needed to infiltrate. This, in turn, results in a higher rate of sickness.


Some 53,000 North Vietnamese are accepted as having infiltrated into South Vietnam during 1966. About 75 percent of these—39,750 came through Laos—the rest through the Demilitarized Zone. Since the evidence shows that about 20 percent of those starting the trek never reached South Vietnam, this would indicate that some 49,687 left the North via Laos in 1966 and 9,937 were lost en route. A similar computation using the total of 81,000 infiltrators which includes both “accepted” and “possible” categories would indicate that about 15,000 may have been lost in 1966 en route through Laos.

Figures on infiltration through the Demilitarized Zone are inadequate to make a meaningful comparison. Reports on three units totaling 740 men have been received which mention losses en route. The loss rate for these three units runs at about ten percent.

Table I summarizes the data used for the estimates in this report.2 Evidence on about 7,000 infiltrators in 11 units varying in size from company to regiment made up the data base for the Laos route. Four units with a total of 1,777 men infiltrated during the last half of 1965 and seven units with a total of 5,390 men infiltrated throughout 1966. The information on losses was derived from those interrogations of captured infiltrators which are immediately available. Poor interrogation methods caused gaps in information and, as a result, the data base for estimating each of the four categories of causes is considerably less than the total number of infiltrators. To produce estimates of permanent losses it is assumed on the basis of limited evidence that half of all deserters eventually are returned to duty and that two thirds of the men who drop out of their units during infiltration are eventually returned to duty.

  1. Source: Johnson Library, National Security File, Country File, Vietnam, Memos to the President, Vol. II, 8/3–27/67. Secret. The notation “L” on the memorandum indicates that the President saw it.
  2. Not printed.