20. Memorandum From the President’s Assistant for National Security Affairs (Brzezinski) to President Carter1
SUBJECT
- Mobile M–X Land Requirements
Secretary Brown has sent you a memo (Tab A) describing the status of the land on which a mobile M–X system might be deployed.2 You will note that he calls attention to the politically-volatile environmental impact issue as well as the question of whether a mobile M–X is technically feasible.
Since the memo did not appear to be time urgent, my staff delayed sending it forward in order to include some additional perspectives on the M–X land requirement issue based on analyses done as part of NSC/PRM–10.3 Unfortunately these analyses were very contentious and led to the long delay in forwarding Secretary Brown’s original memo.
Secretary Brown’s memo provides a conceptual layout of 200 seven nautical mile long trenches at the Luke Gunnery Range and Yuma Proving Ground in Arizona. Each trench would contain one M–X. Analyses of M–X survivability undertaken as part of PRM–10 indicate that if the Soviets attacked this system (and the US silo-based ICBM force) with their projected 1986 ICBM forces in an attack designed to minimize surviving missiles, the number of surviving US ICBMs would be:
| Fraction of SovietICBM Force Expended | Approximate Number of Surviving M–X ICBMs | Approximate Number of Surviving Silo-Based ICBMs |
| [3 columns, 3 rows not declassified] | ||
These results assume that: (1) Soviet ICBM reliability is about 80 percent, (2) the Air Force is able to meet its goal of a [less than 1 line not declassified] hardness level for the encapsulated missile, and (3) an effective method can be found for nullifying the “shock tube” effect that will occur if the blast waves “get into” the tunnel. (If this occurs, the tunnel will act as a classic shock tube and propagate overpressure levels to substantially greater distances than would otherwise be possible.)
Subject to these uncertainties, the surviving ICBM forces in the above table would still have the capability to do substantial damage to the Soviet Union, but not nearly the level of damage we would prefer in each leg of the strategic Triad. Thus we will probably need more than the 1400 nm of trenches at Luke/Yuma if a trench-based M–X system is to guarantee a significant survivable ICBM force.
- Source: Carter Library, National Security Affairs, Brzezinski Material, Subject File, Box 42, Missiles: 2–6/77. Secret. Sent for information. Carter initialed the top of the memorandum. Molander and Utgoff sent the memorandum to Brzezinski for his signature under a June 13 covering memorandum.↩
- Attached but not printed is a May 5 memorandum to Carter, from Brown, who wrote: “Here is some information on possible basing of M-X, which puts the ‘trench’ problem in context. The technical workability still needs to be argued convincingly. Moreover, environmental concerns will still exist. My evaluation: not impossible (as thousands of miles of trench in an extended publicly used area would be) but the feasibility, technical and political, is by no means proven.”↩
- See Document 3.↩