In May 1977 the Fleet Requirements Committee wanted twenty-four SSN and nine SSK (conventional submarines). It envisioned five SSN on surveillance duty north of the GIUK Gap and another five attacking Soviet submarines passing through the passive (SOSUS) surveillance area around the Gap. Another three would be employed to mark (and engage) Soviet surface ships moving south into the Atlantic to attack shipping. Four more would support the British SSBN force. Finally, seven would employed in direct support of British surface groups. Of the diesel submarines, five would be employed in the barrier in the Gap and another four would be employed supporting SSBNs and in the shallow seas.
By 1983 the direct support mission was gone. The requirement was now twenty-seven active SSN and thirteen active SSK, backed by another seven SSN and four SSK in refit. Many more SSN were now to be forward-deployed: four in the Barents Sea and eleven in the North Norwegian Sea, with another five in the South Norwegian Sea and the GIUK Gap. One was assigned to the South-west/North-west Approaches and four to defence of shipping. Of the SSKs, two would be in the North Norwegian Sea, eight in the South Norwegian Sea and the Gap, two in the South-west/North-west Approaches and one would be assigned to defence of shipping. Given actual numbers available, this was most unlikely to happen.
The declared NATO requirement for 1985-90 listed four SSN as a flank barrier, another eight conducting area ASW, two in the North-west Approaches and two for augmentation, plus four refitting. The SSK requirement was six for area ASW, five in the GIUK Gap, one in the North-west Approaches, two for augmentation and three refitting. That made for a total of twenty SSN and seventeen SSK, the former being attainable but the latter entirely unrealistic. In 1985 the Royal Navy had thirteen SSNs in service; plans called for that to increase to eighteen in 1991, after which it would decline without service extension. At this time the planned 1985 SSK force was fifteen submarines, including the remaining rebuilt Oberons. Without some special measures, the SSK force would begin to decline in 1988. (pp. 163-4)