Chances of US bombers penetrating Soviet defenses in the 1960's – 85 percent

In a memorandum from Defense Secretary McNamara to President Johnson in December 1966, it was footnoted that “it was generally agreed within the United States Government, that approximately 85 percent of the U.S. incoming bombers could penetrate the Soviet defenses and reach their targets.”

http://history.state.gov/historicaldocuments/frus1964-68v10/d160

160. Draft Memorandum From Secretary of Defense McNamara to President Johnson1

Washington, December 22, 1966.

SUBJECT
Production and Deployment of the Nike-X

(snip)

The Soviets for more than a decade have spent substantially more on air defense against strategic bombers than has the U.S. The bulk of the Soviet expenditure has been wasted – throughout the period the U.S. Strategic Air Command stated, and it was generally agreed within the United States Government, that approximately 85 percent of the U.S. incoming bombers could penetrate the Soviet defenses and reach their targets. [Footnote in the source text.]