During World War II, German intelligence spread its tentacles across the globe, operating throughout occupied and neutral Europe, and even as far afield as the United States. Discover how German intelligence proved a formidable foe, and how, in the end, it was totally compromised from its centre.

Berlin has always been a hotbed of espionage. Uncover the secrets under the Kaiser, during the tyranny that was Hitler's Third Reich, and throughout the long Cold War that followed the destruction of the Nazi empire by the Allies.

An unprepossessing Victorian Mansion 50 miles north of London, Bletchley Park started life as Station X before developing into the most potent deciphering center of World War II when the German Enigma codes were cracked by its staff.

Established by President Truman, the CIA became a global agency for collecting and evaluating intelligence through covert action. It has a fascinating history throughout the post-war world to the modern day.

The fascinating story of 20th-century efforts by all sides to break down the enemy's signals security, to protect the sender's signals, and penetrate the enemy's secret communications. Many battles in the last 100 years have been won or lost because one side or the other could read its opponent's intercepted messages. From the famous Zimmerman Telegram in April 1917 through to the breaking of the Japanese Purple codes and the more recent Russian codes, trace the history of code breaking.

The FBI serves as a national police force investigating interstate crime. However, it also handles violations of U.S espionage laws by foreign agents. Probe the department's entire history, including the G-man era, interception of Nazi agents, communist-hunting in the 1950s, the search for subversives, and its role in the post-Cold War world.

Born in the crucible of Israel's war of independence and honed in the constant struggle for survival, the Mossad gained a fearsome reputation for ruthlessness. Whether tracking down criminals like Adolf Eichmann or eliminating terrorists like the Palestinian Black September movement, discover how Mossad allowed nothing to stand in its way.

During both World Wars, Britain's counter-espionage service proved highly effective - no enemy spies operated for more than a few days, and many were "turned" to send false intelligence back home. Later, MI5 faced criticism for failing to expose the Cambridge spies, then remodelled itself as a counter-terrorist organisation.

Britain's Secret Intelligence Service, and employer of the fictional James Bond, grew out of the need to combat imperial German and later Bolshevik ambitions in the early part of the 20th Century. Uncover the secret workings of MI6, and see how its spectacular successes, like breaking the Enigma code, were offset by devastating failures such as the inability to detect superspy Kim Philby.

This episode focuses on the Komitet Gosudarstvennoe Bezopasnosti (Committee for State Security), the agency of the former Soviet Union responsible for state security from 1954 to 1991. KGB functions included counterespionage, foreign intelligence collection and analysis, protection of land and maritime borders, control of nuclear weapons, and the Kremlin's guards.

One of the Soviet Union's greatest espionage operations ended in 1951 when two diplomats at the British Foreign Office fled from Southampton Dock. Uncover the story of one of the most effective spy rings of all time as they passed along military, scientific, and political secrets that caused incalculable harm to British and American interests.

Britain's secret wartime Special Operation Executive was responsible for recruiting and training hundreds of secret agents, who were systematically dropped into Germany and Nazi-occupied Europe to fight the enemy behind the lines. By setting up clandestine radio transmitters and organising local spy rings, see how they undoubtedly hastened the end of WWII in Europe.

Take a look at America's Office of Strategic Services, which was modelled on the British Special Operation Executive. William J. Donovan established the famous U.S World War II intelligence and sabotage agency, which was the precursor of the CIA. Much of the OSS work concerned the Allies' landings in North Africa and Europe, the placing of nearly 200 agents in Nazi Germany, assisting French resistance groups, and working in the Far East against the Japanese.

In one of the deadliest and most difficult conflicts the world had ever witnessed, straightforward warfare was not enough. The Vietnam War demanded secret fighting. This is the story of the covert operations conducted by the CIA and US army intelligence. By employing tactics such as harassment, espionage and covert sea-born raids, the Americans weaseled out the enemy.

Mata Hari, Sidney Reilly, Lawrence of Arabia, Cicero, Lonsdale, the Lucy Spy Ring: these are just a few of the most daring and outrageous spy cases in the 20th Century.

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 the US. The success of this operation enabled the Russians to detonate 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 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 also 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 30s, 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.

At the beginning of the 20th century, the French had a sophisticated intelligence network active during World War I, which went on to confront the Bolsheviks during the interwar years. It continued during World War II and has since been involved in post-war intelligence and various colonial conflicts.

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.