At the beginning of the Cold War, the gathering of intelligence on the Soviet Union's current and future military capability seemed a near-impossibility. Soviet high-level communications were secure against decryption. Agent networks in the USSR were very difficult to establish and of uncertain reliability. Aerial reconnaissance of warrelated targets in the Soviet Union was risky and could only be occasional. But valuable intelligence was gathered in the years 1945-55 on the USSR's frantic arms build-up, thanks to its policy towards Germans and their country. Its exploitation of Germans and its Zone of Germany in its war-related research and development and the reconstruction of its war-related industries gave British Intelligence penetrable targets in the Soviet Zone and gave great numbers of Germans sought-after information on the USSR itself. The ease of recruiting age nts in East Germany and the flight (including enticed defections) of refugees from it allowed research and development projects and uranium.-mining operations there to be penetrated. Intelligence of Soviet weapons development and of the quality of Soviet military technology was obtained. The mass interrogation of prisoners-of-war returned by the Soviets to the British Occupation Zone in the late 1940s yielded a wealth of valuable information on war-related construction and the locations of numerous intelligence targets in the Soviet Union: most importantly, those of atomic and chemical plants, aircraft and aero-engine factories, airfields, rocket development centres and other installations. When, in the period 1949-58, some 3,000 deported German scientists , engineers and technicians were sent back to their homeland from the USSR, promising sources among them were enticed West and interrogated for their knowledge of the Soviets' research and development projects. The cream of the information they provided was crucial intelligence on the locations of atomic plants and laboratories and uranium deposits; useful information on structural weaknesses in the Soviet system of scientific and economic management; expert (if out-of-date) assessments of the quality of Soviet accomplishments in atomic science, electronics and other fields; and well-informed indications as to possible lines of development in guided missile and aircraft design. One Soviet scientific defector in Germany provided similar information which influenced British perceptions of the Soviet Union's scientific potential and missile development plans. Refugees entering the British Zone from East Germany, intercepted letters and monitored telecommunications, informal contacts and, of course, secret agents all made significant contributions to the gathering of scientific and technical intelligence in Germany too. The British passed to the Americans much of the intelligence they acquired in Germany and the installations identified and located by German sources were overtlown by spyplanes in the 1950s and particularly by U-2s in the latter half of-the decade. Priceless information was obtained, which establi shed that the USSR's war-related scientific research and development and its actual military capability were both inferior to those of the West. Thus the Germans enabled Soviet security to be deeply penetrated and helped to stabilize the Cold War. They are the missing link between Ultra and the U-2.