Pages 50-64 from Nixon. NSSM. Box H-182

This Analytical Memo on NSDM 123 states among the following: 

The study notes that the UK nuclear force makes a relatively small contribution to US strategic objectives. All UK strategic forces, when assigned to NATO are targeted solely against military targets, contributing currently about seven percent of the total coverage. The proportionate UK contribution will shrink even further as Poseidon enters the US force. Moreover, targets programmed to be struck by the UK are also programmed to be struck by the US in order to achieve the required damage expectancy and to hedge against the unavailability of the UK force. Under the Nassau Agreement, Britain retains the right to withdraw its force when "supreme national interests" are at stake. Under such circumstances, it is presumed that the UK maintains independent strike plans directed against Soviet urban targets. In short, the design objective which the UK has set for Super Antelope (penetrating the Moscow ABM) is more relevant to the national purposes of the UK Polaris force than to the role of that force in NATO strike plans. Moreover, an independent UK launch capability diminishes our control over the initiation and conduct of nuclear war, and thus poses a potential inconsistency with US objectives.

If US assistance to the UK on Super Antelope became known in Moscow, the Soviets could charge that we were "circumventing" a SALT agreement by aiding a third country in the development of strategic arms. The Soviets could be especially sensitive since the objective of Super Antelope is to penetrate Soviet ABM defenses. This might make more difficult the task of negotiating a limitation on ABM's.