175. Letter From Director of Central Intelligence Helms to the President’s Special Assistant (Rostow)1
In SNIE 11–10–672 we used, as usual, some verbal expressions to describe our estimated capability to detect land mobile ICBM’s, IRBM’s, and MRBM’s, and new missile–launching submarines in the USSR. You asked that we give you a translation into number.
First with regard to Land Mobile ICBM’s, IRBM’s, and MRBM’s:
We can quote no discrete odds for detection in the early stages of deployment. Our word “possible” in this context simply means that we are not certain of being able to detect nor do we feel it is impossible that we will detect. Your mathematical friends define this use of “possible” as “non–zero probability.”
As to extensive deployment of these weapons systems we feel our chances of detecting are greater than even and less than overwhelming—say in the general bracket 65% to 85% Second, with regard to Missile–launching Submarines:
As to detecting units of an entirely new class before IOC, we have put the odds in the 65% to 85% bracket.
As to detecting new units of an existing class before delivery to the fleet, we put the odds about even; 50–50.
The enclosed article which Sherman wrote some time back may further enlighten.3