Allied intelligence gathering in Berlin by the three allies present in the city: the British, the Americans and the French. British intelligence-gathering activity in Cold War Berlin was initially focused at Royal Air Force (RAF) Gatow, the British occupation force’s airfield, a former Luftwaffe training base located at the western extremity of the British occupation zone, with part of its boundary set against the sector boundary with the East. The electronic intelligence surveillance team moved over to Block 15 at this time, and again was accommodated in a wooden hut on the roof. For the remainder of the decade and into the early 1960s the upper floor of the Hanbury Block was the centre of intelligence-gathering operations, with the RAF unit located on one side of the corridor and an army unit opposite. The chapter also presents an overview of the key concepts discussed in this book.