PMN1 asked the same question in another place, and I replied there.
But for the benefit of this forum:
Friedman's account of the reasons behind the decision not to install a stellar-inertial guidance system for the Poseidon may not be completely accurate. At one stage, the US DoD fully backed the idea.
In the draft of a 1 December 1967 memorandum to President Johnson, US Secretary of Defense Robert McNamara recommended “developing a stellar-inertial guidance system for the Poseidon force”, and stated that “The JCS and the Secretary of the Navy concurred in the development of a stellar-inertial guidance system”
Opposition to the scheme seems to have come from the US State Department. As I have posted in another place, in his ‘Aerospace Memoirs’, Art Lowell recalls that when he was Assistant General Manager, Polaris Program...
“By Kissinger State Dept. fiat, SSPO [US Navy Strategic Systems Program office] was not permitted to have such accuracy in its FBM [Fleet Ballistic Missile], for fear the Soviets would believe that we were preparing for a first strike against them.
"By the time of Trident, however, the FBM system had been released from this restraint, its mission defined to include ''counterforce'', and SSPO was permitted to make improvements in its submarine navigation systems, and add stellar tracking to the Trident's guidance system (we’d had a stellar observation window in Poseidon all along, but were not allowed to add the tracking components.)”
Mercurius Cantabrigiensis
