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The balloon first gave mankind the ability to look down on the battlefield; then came ever more sophisticated aircraft with cameras. Today much of the work of intelligence gathering is undertaken by satellites. The fascinating story of spying from the air over the last 100 years, including the hitherto untold story of the secret spy flights of the Cold War.

During World War II the Soviet government operated a large spy ring that sought atomic secrets in Great Britain, Canada and USA. The success of this operation enabled the Russians to explode an atomic bomb several years earlier than believed possible. Not until the US 'Venona' code-cracking breakthrough was the full extent of the Soviet penetration revealed.

The Cheka was the infamous Bolshevik organisation which took control of Russia as Lenin's feared secret police. It was licensed to carry out executions and was responsible for the 'Red Terror' from September 1918. Its brutality knew no bounds and it was run by the dreaded Felix Dzerzhinsky who founded the Gulag Archipelago.

Aircraft were first used to drop agents behind enemy lines during World War I. The skills of the first pioneers were rediscovered twenty years later when Britain had to find ways of supporting Resistance throughout Nazi-occupied Europe. Agents were flown in or picked up, supplies and sabotage teams parachuted. The British Special Operations flights were joined by US 'Carpetbagger' squadrons, and their methods continued to be employed during the Cold War.

This organisation traces its roots back to 1776 and the spying service set up by George Washington. Since then the service has distinguished itself throughout the Twentieth Century, with exciting stories of intelligence gathering in both World Wars and during the Cold War and Vietnam, culminating in its electronic intelligence units which were first used in the Gulf War in 1991.

From its early beginnings with General John J Pershing and his Mexican expedition of 1916, the US Air Intelligence arm has a fascinating history, spanning both World Wars. It is now the world leader in the collection and analysis of all forms of photographic and electronic data, and deploys a bewildering array of ultra-high speed aircraft, satellites and unmanned drones.

Sometimes referred to as the 'Fourth Department, Russian military intelligence', it was created in 1918 and produced a network of spies which operated worldwide through the Stalinist era, World War II and still employs 100,000. The GRU also controls Russia's Special Warfare Services known as the Spetsnaz.

Throughout the Twentieth Century in all the major conflicts both sides have operated intelligence collection ships. In World War II the warships of many navies began carrying high-frequency, direction-finding equipment and subsequently electronic intelligence collection equipment. But there have been a fascinating array of non-naval vessels. Some of them like the USS Pueblo have been involved in major international incidents. Others have mysteriously disappeared.

Japan's traditional fascination with the West led at the beginning of the 20th century to the foundation of an elaborate spying network based on the need for military intelligence. Historically its enemies were China and Russia but by the 1920s and 1930s its main focus became the USA. The programme looks at the story of the Japanese intelligence network in the build up to Pearl Harbor and beyond.

Already in position at the beginning of the 20th Century the French had a sophisticated intelligence network which was actively useful during World War I and which went on to confront the Bolsheviks during the inter War years. It continued during World War II and has since been involved in post war intelligence and various colonial conflicts which have provided a fascinating story.

The US's longest surviving intelligence service was created in 1882. One of its most prominent divisions was the American Photographic Interpretation Centre created in 1941 to train and support fleet photographers. It played an active role in the Cold War era particularly in electronic monitoring. By 1970 a vast expansion in Russian Naval operations on a worldwide scale created the necessity to keep track of all Soviet naval-related activities.