Foreign Relations of the United States, 1964–1968, Volume IV, Vietnam, 1966

255. Memorandum From Secretary of Defense McNamara to President Johnson¹

Washington, October 3, 1966.

SUBJECT

• Naval Gunfire Against North Vietnam

On a number of occasions since May of this year, General Westmoreland and Admiral Sharp have recommended the use of naval gunfire against North Vietnam. These recommendations have had the support of the Joint Chiefs of Staff, but have never received final approval, largely because of the international problems such action might entail. At present, naval fire on North Vietnam is authorized only in self defense against attack from the shore.

As you know, General Westmoreland is now quite concerned about the threat developing to the northernmost provinces of South Vietnam—in the form of enemy attacks supported, and potentially launched from, the DMZ and southern portions of North Vietnam. He is urgently requesting authority to employ naval gunfire against North Vietnam south of 175 30ʼ—i.e. from Dong Hoi south to the DMZ. Again, he has the support of CINCPAC and the Chiefs. The advantages and disadvantages of approving this request are briefly set forth below.

1. Advantages. General Westmoreland and the Chiefs point out that the enemy buildup in and north of the DMZ involves numerous fixed military targets and a vital supply axis along coastal Route 1, supplemented by waterborne traffic, all of which cannot be consistently and successfully engaged by air attack. Naval gunfire is less inhibited by darkness and weather than is tactical air. It can deliver reasonably accurate area and harassing fire under any weather conditions. It can engage targets, including moving targets, with observed fire in weather which would preclude effective air attack. In good weather, its accuracy at reasonable ranges is equal to that of air attack.

Operating within 12 miles of the coast, the various ships and weapons involved can effectively engage targets up to 12 or more miles inland—a distance which encompasses the principal lines of communication in that part of North Vietnam and the eastern portions of the DMZ. At least in theory, the application of naval gunfire to targets in this area would free tactical air resources to engage targets along the more primitive LOCʼs to the west, in the western DMZ, and in the immediate battle area of any actual attack. Also, ships could be used to engage targets which the enemy has protected with heavy local defenses and thus avoid aircraft losses. (It is always possible, of course, to lose a ship to coastal guns or air attack.)

This fire could be provided with resources already deployed, at the expense of support to forces in South Vietnam. Ammunition supplies are adequate. The most probable average commitment would be 4 ships (one 6" or 8"-gun cruiser, two 5"-gun destroyers, and one 5"-rocket ship) of the 7 to 11 such ships which have been engaged in naval gunfire support to operations within South Vietnam. On a number of occasions, this in-country support has been quite effective.

In sum, the arguments in favor of employing naval gunfire against North Vietnam are: a serious threat exists involving targets appropriate for naval gunfire; the resources are readily available; and this fire can be delivered under certain conditions which preclude air attack. The Joint Chiefs of Staff have recommended that we approve the use of naval gunfire south of Dong Hoi against radar and antiaircraft sites, other fixed military targets, convoys and elements of LOCʼs and North Vietnamese craft which are definitely identified as naval vessels or vessels bearing military cargo. Attack would be prohibited against civilian craft and other targets which involve large collateral damage or civilian casualties.

2. Disadvantages. The disadvantages of this course of action still lie primarily in the reactions we may expect from the North Vietnamese, the Chinese, other nations, and certain elements here at home. There is also some doubt as to the measure of military advantage we would gain to offset these reactions.

While from one point of view the additional destructive force applied against North Vietnam by naval fire would be proportionately small, from another viewpoint this would be escalation, and a step toward extension of naval bombardment still farther north. The enemy probably would claim that we were engaging in a new kind of attack. Perhaps more important, since this is the kind of activity which would normally precede such action, the North Vietnamese and Chinese might conclude that we were in fact preparing to invade the North, and undertake some escalatory action in response. (At the very least, this action would lend credence to past South Vietnamese threats and American newspaper speculation concerning invasion.) Other nations, including some allies, would probably regret that we found this new departure necessary, and might dissociate themselves from it. International legal questions could be raised. It is certain that at least some of our detractors here at home would point to the action as a new and serious form of escalation. On the other side of this question, it must be conceded that our ships have already fired on North Vietnamese territory—in defense against shore fire—on three occasions (February, March and April of this year while engaged in search and rescue operations). There was no serious adverse reaction in these cases, but the self-defense nature of the fire was immediately demonstrable.

We have no guarantee that the incremental military benefits of naval gunfire would be of sufficient magnitude to compensate for these adverse reactions. Assuming that sufficient targets can be identified, ships engaged in this mission would probably fire on the order of 200 rounds per ship per day, or a total of 800 rounds.

• —As one measure of the concentration involved, this would amount to 16 rounds per mile over the 50-odd miles of Route 1 from Dong Hoi to the DMZ.
• —As another measure of weight of effort, the explosive charge in the average round involved is on the order of 14 pounds. This would mean about 6 tons delivered per day—quite a small amount (roughly the equivalent of 10 attack sorties) compared with tonnages we have delivered in the same area with tactical air.
• —The average shell has an effects radius of 40–90 yards against personnel, and a somewhat smaller radius against vehicles. Some types can achieve good penetration of concrete and other fortifications, particularly if the target presents a vertical face, but this requires precision, observed fire.
• Granted, this weight of effort could be concentrated (especially that of the rocket ship), or substantially increased (by committing more ships or by including a higher proportion of heavier guns). Even so, when we consider the large amounts of tactical air available—particularly in an emergency—and the rather limited sets of circumstances under which naval gunfire enjoys an undisputed superiority, the military advantages appear less imposing.
• —Few fixed targets would be so time-sensitive as to demand attack during weather conditions when naval ships could engage them and tactical air could not.
• —At least half the problem with fleeting targets, such as convoys, is to locate and identify the target; this part of the problem would be the same for naval fire as for tactical air. This detracts from the admitted ability of naval ships to engage a target, once located, under certain conditions when tactical air would not be effective.
• —While the enemy may undertake to increase antiaircraft defenses in southern North Vietnam to support a major effort, at present his defenses in that area have been neutralized to the point where we lose relatively few aircraft.

3. Recommendations. On balance, I conclude that the military advantages of approving naval gunfire against North Vietnam at this time are outweighed by the probable adverse reactions and possible military risks. The Secretary of State and I recommend against approval.

Robert S. McNamara²

1. Source: Johnson Library, National Security File, Memos to the President—Walt W. Rostow, vol. 14. Top Secret. Rostow forwarded the memorandum to the President at 9:30 a.m. on October 4 under cover of a memorandum stating that he concurred with McNamaraʼs recommendation. (Ibid.) During a telephone conversation with McNamara that began at 7:48 a.m. on October 5, the President indicated that he had read McNamaraʼs memorandum and thought his decision was justified but also thought McNamara should get the Joint Chiefs and their adherents to point out how disastrous it would be for the United States to inaugurate a new policy of this type during the closing days of Congress and on the eve of the Manila Conference, and “how the propaganda people would just wreck us.” (Ibid., Recordings and Transcripts, Telephone Conversation between Johnson and McNamara, Tape F66.27, Side B, PNO 2)
2. Printed from a copy that bears this typed signature.