William John Christopher Vassall (20 September 1924 – 18 November 1996) was a British civil servant who spied for the Soviet Union, allegedly under pressure of blackmail, from 1954 until his arrest in 1962. Although operating only at a junior level, he was able to provide details of naval technology which were crucial to the modernising of the Soviet Navy. He was sentenced to eighteen years' imprisonment, and was released in 1972, after having served ten. The Vassall scandal greatly embarrassed the Macmillan government, but was soon eclipsed by the more dramatic Profumo affair.