For a long time after the discovery that the Soviet Union had been given the secrets of the atomic bomb by men on the Manhattan Project – German, American, Canadian and Italian – an argument raged as to whether this factor was more important than the indigenous efforts of Russian physicists.

No one could deny their undoubted skills. It is just that the United States did not expect Stalin to have the bomb before 1955. The fact that the bomb was tested at the end of August 1949 had a shattering impact in Washington DC as it wrecked expectations that the postwar balance of power would remain to American advantage. And, on the back of revelations about those spying for Russia, it launched an era of right-wing intolerance that stained America’s reputation into the 1960s, when even foreign socialist novelists like Gabriel Garcia Marquez were shut out under the McCarran-Walter Act of 1950. So all this is as much a matter of recent American history as the history of Russia.

The explanation for the speed with which the Russians caught up lay in the extraordinary, if not brilliant efforts of Soviet foreign intelligence under the inspired leadership of Pavel Fitin. Only since the 1990s have those efforts been heralded as critical to the Soviet achievement. Poor old Fitin was abruptly discarded after the war, having crossed the dreaded Lavrenty Beria once too often, initially over the value of atomic research, which Fitin intuitively understood.

It is reported that the entire collection on Soviet atomic espionage amounts to 17 volumes in the archives of the foreign intelligence service (SVR). Finally, perhaps, we will learn in much greater detail how the Russians managed to penetrate the atomic project from its early beginnings in Britain through to its high point in the United States.