132. Memorandum From Fritz Ermarth and Victor Utgoff of the National Security Council Staff to the President’s Assistant for National Security Affairs (Brzezinski) and the President’s Deputy Assistant for National Security Affairs (Aaron)1
SUBJECT
- M-X Basing PRC (U)
There is a new contender in the field: Open trench/rail mobile! Awaiting the full PRC, those gathered in the Sit Room on 9 May2 heard Bill Perry preview what he had planned to present. He covered the following:
1. Open Trench/Rail Mobile M–X Basing
The rail mobile variant of Option 5 (DYAD with 300 D–5s in silos and 100 on trains) has evolved into a distinct basing option for the M–X. The concept is very like the hybrid trench, except that the trench and appropriately spaced hardened shelters along the trench can be opened to overhead inspection. Ease of verification results. Ability to move missiles rapidly on the rails in the trench, even on tactical warning, makes long-lasting denial of location information less critical than in MPS. If necessary simulators could be used to defeat close-in sensors. (S)
In principle, this concept could be as survivable as MPS. Verifiability on the US side is more easily achieved than in MPS, and is probably easier on the Soviet side. On the other hand, impact on public use of land and on the environment is probably more severe than with MPS. This was one of the several factors that removed the open trench from consideration over a year ago. (S)
In the discussion it was pointed out that costs and environmental impact might be reduced by laying the track between shelters at ground level, but security and location secrecy might be made more difficult. It was noted that our selection of this concept would not constrain the Soviets to it (this applies to any concept). Open trench might be less susceptible to Soviet breakout within the basing system than MPS would be. But it might, like MPS, give the Soviets an incentive to proliferate RVs covertly, which they could deploy outside any multiple shelter system. Clearly, if limiting force size is important for arms control and stability, we need controls on system production in SALT. (S)
[Page 610]Davy Jones observed that, in the JCS view, open trench was next best to MPS and clearly preferred over putting improved missiles into silos. (S)
2. Incremental Costs
The open trench concept would, as Perry described it, be very roughly $3B more expensive than the baseline MPS concept. If the D–5 (fully common missile) were deployed in place of the M–X, in either MPS or the new trench concept, it would cost yet an additional $1B because a larger number of D–5 missiles would have to be deployed to achieve the same level of surviving RVs as afforded by the M–X. On the other hand, later procurement of the D–5 for Trident deployment would be much cheaper. (S)
3. The Case for Trident II.
Perry also argued that, whatever is done about ICBM development and basing, it makes sense to develop and deploy the Trident II missile. Apart from the greater operating area and resultant increases in SSBN security afforded by the Trident II’s range, its larger payload would allow us to maintain the current SLBM RV levels with 6 fewer Trident subs—resulting in more than enough savings to pay for the larger missile. (S)
The Navy is clearly not enthusiastic about Trident II—but some elements of OSD clearly are. Queried on prospects for SLBMs becoming accurate enough to be silo killers, Perry said he thought SLBM [less than 1 line not declassified] could possibly be attained in 10 years. This might or might not be sufficient to make the MK–12A a silo-killer; uncertainties about Soviet silo hardness deny confidence that this CEP is sufficient. Perry was confident however that the D–5 missile can be made accurate enough to be a good hard target killer when deployed on land. (S)
The attractions of the open trench concept are considerable. It should be examined more carefully, particularly with respect to environmental impact, before Harold makes his final recommendation. (S)