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Sentinel

At the request of Secretary of Defense McNamara, the US Army worked up a deployment plan aimed specifically at the supposed Chinese threat. It was believed then (1967), based on the Chinese nuclear test program, that China could have a few operational ICBMs in the early 1970s.

This deployment plan was presented in July 1967. It consisted of several PARs across the northern boundary of the United States and Alaska to perform the long-range detection and acquisition function; MSRs and SPARTAN batteries in the continental United States and Alaska, and one MSR and SPRINT battery in Hawaii. The deployment required several hundred SPARTANs for overall defense and a lesser number of SPRINTs to defend the PARs.

The entire country was thus given en area defense against a first-generation threat. Deployment of some of the complement of MSRs in Minuteman fields provided an option to give some of the Minuteman forces a high quality terminal defense by installing SPRINTs in these fields later.

The investment costs (excluding research and development and tactical operation and maintenance) were estimated to be in the vicinity of $5 billion. In September 1967, McNamara announced a decision to go ahead on this deployment. It was subsequently named SENTINEL.

The SENTINEL proposal was widely criticized, and after the presidential election the incoming administration Nixon's set up a review of the whole defense concept.

Draft Memorandum From Secretary of Defense Clifford to President Johnson, dated July 29, 1968, reviewed Strategic Offensive and Defensive Forces for FY 70-74. It noted that a defense of the programmed Minuteman force could use the same components being developed for the Sentinel system: Sprint, Spartan, Perimeter Acquisition Radar (PAR), and Missile Site Radar (MSR). An option for a light defense of Minuteman is being maintained in the current Sentinel deployment plan. This light defense, although not increasing the number of Minuteman surviving a heavy Soviet attack, might show our determination to protect Minuteman and indicate that we would expand the defense if the threat grew larger. In a less than all-out attack on Minuteman (about 1,200 reliable, accurate re-entry vehicles), the light defense could save about 300 Minuteman missiles. The median defense would be an expansion of the light defense to defend more Minuteman and could be supplemented with additional Minuteman III in hard rock silos. The ABM defense and hard rock silos would insure enough Minuteman surviving against large MIRVs on the SS-9 to maintain, together with our other forces, our Assured Destruction capability. The heavy defense of Minuteman would maintain our Assured Destruction capability even against a Soviet small-MIRV threat. The table on the next page summarizes the three levels of defense.

Levels of Minuteman Defense

Defense

Sprints

Spartans

MSRs

Defense Investment Cost/a/
($ Billions)

Level-Off Annual Operations Cost/a/
($ Millions)

Light

320

120

4

$0.4

$ 30

Median (With Hard Rock Silos)

1,480

120

15

3.9/b/

310

Heavy

2,220

120

15

4.4

380

/a/Assumes the deployment of Sentinel. Fifty-six Sprints, 120 Spartans, and four MSRs are deployed as part of Sentinel.

/b/Does not include the cost of hard rock silos.

"A defensive system to save U.S. cities from a Soviet nuclear attack must attempt to keep ahead of the Soviet threat, including their reactions to our deployment. Such attempts are costly. In our analyses we use two stages in such a deployment./2/ The first, "Posture A," is an initial step recommended by the JCS. It represents an area defense of CONUS and a light defense of 25 cities. It would cost about $12 billion in investment and $900 million a year to operate. The second, "Posture B," is an attempt to keep ahead of the threat. It includes a higher density local defense of 52 cities. It would cost about $20 billion in investment and over $1.2 billion a year to operate. For Posture B we would also need improved air and civil defenses and ASW forces at an additional cost of $4 to $5 billion in investment. We believe the pursuit of effective defenses would eventually cost much more. Our commitment would be open-ended."

MacNamara then turned to Damage Limiting Against the Soviet Threat. The language in this section is very similar to that presented in Enthoven and Smith, How Much Is Enough?, pp. 188-190, it is likely that these paragraphs and tables (not to mention much of the rest of the document) were drafted in the Systems Analysis Office headed by Assistant Secretary of Defense Enthoven. The two tables in the book (pp. 189-190) and the authors' account provide additional information on a U.S. first strike (ibid., passim). Secretary McNamara's statement to the Senate Armed Services Committee on February 2, 1968, also includes a table of U.S. and Soviet fatalities for both a Soviet first strike and a U.S. first strike in the mid-1970s. See Authorization for Military Procurement, Research and Development, Fiscal Year 1969, and Reserve Strength: Hearings Before the Committee on Armed Services, United States Senate, Ninetieth Congress, Second Session (Washington: Government Printing Office, 1968), pp. 122 ff.

"Our ability to strike back and destroy Soviet society, even under conditions and assumptions favorable to the Soviets, makes any kind of nuclear war with the Soviets unlikely. Thus, we first buy forces to give us high confidence in our deterrent. As insurance in the unlikely event deterrence fails, we then consider adding forces that might reduce damage to our population and industry. Since we have offensive forces available for attacking military targets, the basic Damage Limiting issue is whether we should deploy Nike-X in defense of our cities.

"A defensive system to save U.S. cities from a Soviet nuclear attack must attempt to keep ahead of the Soviet threat, including their reactions to our deployment. Such attempts are costly. In our analyses we use two stages in such a deployment./2/ The first, "Posture A," is an initial step recommended by the JCS. It represents an area defense of CONUS and a light defense of 25 cities. It would cost about $12 billion in investment and $900 million a year to operate. The second, "Posture B," is an attempt to keep ahead of the threat. It includes a higher density local defense of 52 cities. It would cost about $20 billion in investment and over $1.2 billion a year to operate. For Posture B we would also need improved air and civil defenses and ASW forces at an additional cost of $4 to $5 billion in investment. We believe the pursuit of effective defenses would eventually cost much more. Our commitment would be open-ended."

Deaths In an All-Out Strategic Nuclear Exchange in 1977,
Assuming No Soviet Reaction to a U.S. ABM System
(In Millions)

U.S. Program

Soviets Strike First,
U.S. Retaliates

U.S. Strikes First,
Soviets Retaliate

Soviet Assured
Destruction Calculation

U.S. Killed

Soviet Killed

U.S. Killed

Soviet Killed

No ABM

120

[*]

120

[*]

[*]

Sentinel

90

[*]

100

[*]

[*]

Posture A

40

[*]

40

[*]

[*]

Posture B

10

[*]

10

[*]

[*]

" ... the Soviets lose their deterrent if they do not respond. They would be forced to react to increase their ability to strike back. The Soviets have the technological and economic capability to respond in many ways by: (1) adding MIRVs and penetration aids to their projected missile inventories; (2) adding a mobile ICBM, the SS-Z-2; (3) adding a new, higher payload, mobile missile; (4) deploying additional SLBMs; (5) defending all or a portion of their ICBM force; (6) launching all or a portion of their ICBM force on warning; (7) adding more bombers; or (8) some combinations of these responses. Against Posture A, the Soviets must respond with at least 100 new mobile ICBMs or an equivalent force in order to maintain their Assured Destruction capability; against Posture B, they must respond with at least 500 new mobile ICBMs or an equivalent force. These responses, while restoring their Assured Destruction capability, also restore their ability to kill Americans in a first strike."

Deaths In an All-Out Strategic Nuclear Exchange in 1977,
Assuming a Soviet Reaction to a U.S. ABM System
(In Millions)

U.S. Program

Soviets Strike First,
U.S. Retaliates

U.S. Strikes First,
Soviets Retaliate

Soviet Assured
Destruction Calculation

U.S. Killed

Soviet Killed

U.S. Killed

Soviet Killed

No ABM

120

[*]

120

[*]

[*]

Sentinel

100

[*]

100

[*]

[*]

Posture A

90

[*]

40

[*]

[*]

Posture B

90

[*]

90

[*]

[*]

MacNamara then turned to Damage Limiting Against the Chinese Threat.

"There has been evidence that the Chinese are devoting very substantial resources to the development of both nuclear warheads and missile delivery systems. Within a period of less than three years, they successfully detonated six nuclear devices. Last December, they detonated a seventh device, but this test was apparently a partial failure. These seven nuclear tests, together with their continuing work on surface-to-surface missiles, lead us to believe that they are moving ahead with the development of an ICBM. Indeed, if their program proceeds at its present pace (although there is some evidence it has been delayed) they could have a modest force of ICBMs by the mid-1970s.

"The reasons for deploying an ABM system against the Chinese are: (1) it would prevent damage to the United States in a Chinese first strike; (2) it could increase the credibility of our commitments to defend Asian countries against Chinese nuclear intimidation or nuclear attack; and (3) it could lessen China's ability to drag the United States and the Soviet Union into a nuclear war. In addition, a defense against a light and unsophisticated Chinese threat would not deprive the Soviet Union of its Assured Destruction capability.

"On the other hand, we already have a massive deterrent against a Chinese attack. A Chinese-oriented ABM system might enhance the prestige of the Chinese nuclear program and reduce confidence in the ability of our offensive forces to deter attacks on our allies. Further, it might suggest that we think the Chinese would act irrationally when many believe they would not. Leaving Asia and our Asian bases exposed, this system might suggest that the United States is retreating from Asia to a "Fortress America." Finally, it might keep Asian countries from adhering to a non-proliferation treaty by drawing attention to the threat and causing them to raise demands for their own defense, possibly as a step toward developing their own offensive nuclear capability.

"On balance, however, we believe the advantages of a Chinese-oriented ABM system outweigh the disadvantages. Thus, deployment of the Sentinel system was initiated in September 1967."




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