 A strong supporter of the modernising Conservatism championed by Edward Heath, Buck served as the Under-Secretary for Defence from 1972 to 1974 with responsibility for the Royal Navy, but his fortunes declined when Heath lost the election in 1974, and he managed the unsuccessful leadership campaign for his old friend Geoffrey Howe.Buck then lost his place on the executive of the 1922 Committee, although he later regained it.Nevertheless, he remained a perceptive observer of defence policy, opposing the closure of Colchester's military hospital and other cuts.