1. The Berlin Blockade - Moscow draws the Iron curtain

2. Berlin was carved into four zones at the end of World War II, each occupied by one of the Allied powers

3. April 1, 1948, the Soviet Union fired the first major salvo of that new conflict when it announced a crack- down on the free movement of traffic into Berlin.

4. Moscow's blockade of Berlin was calculated to oust the western powers who occupied the city with the USSR.

5. Berlin, like wider Germany, had been carved up into four sectors as part of the post-war peace deal worked out by the US, Soviet Union, Britain and France. Each country controlled a sector. Berlin, Hitler's former powerbase and the focus of the Third Reich, had an anomalous position, located as it was deep in the heart of the Soviet-controlled part of Germany.

6. It amounted to a capitalist presence in the heart of a communist regime - a trophy for the western Allies but a mounting embarrassment to Moscow. While the Soviet Union was busy spreading its influence across eastern Europe, its former wartime allies were moulding their chunk of Germany into a free market, self- governing democracy.

8. Air access only Their plans to launch a west German Deutschmark effectively scuppered any semblance of economic unity. The move infuriated Russia which resolved to force its former allies out of Berlin for good. In truth the former capital had been under siege long before the start of the blockade in spring 1948. The only official access was along one of three 20-mile wide air corridors.

9. Stalin was determined to oust the western powers

10. Getting to Berlin by road or rail depended on the continuing co-operation of Soviet authorities. It meant west Berliners depended on Russian goodwill for deliveries of food, fuel and just about everything else. East-West relations had deteriorated as each side vigorously pursued its own political course and on April 1 1948 Russia, under the leadership of Joseph Stalin, announced stringent controls on all overland traffic from western zones into Berlin.

11. Initially Moscow's tactics seemed to be based on little more than petty-minded bureaucracy. There were obstructions at crossing points, endless delays before trains could pass through signals, fussing over papers and roadblocks. The uncomfortable reality, that the population of western Berlin were at the mercy of the Soviets, dawned rapidly.

12. Blocked but not beaten, the airlift begins

13. Britain, America and France were effectively shut out of the former German capital, where each held a zone under its administration, on June 24, 1948. After almost three months of obstructing land traffic from western Europe through communist- controlled eastern Germany, Stalin closed all roads and railways into the western sectors of the city. Electricity, supplied exclusively from the Soviet sector, was cut off. The blockade had begun in earnest.

14. Moscow's tactics were crude but practical. It planned to "smoke out" the western powers by starving them of food and fuel. Their only way into, and out of Berlin, was by air. Since April, America and Britain had been flying in relatively small cargo loads. There was some debate about forcing the blockade open but the American General Lucius Clay settled on a another tactic and on June 26, the aerial supply mission was stepped up.

15. Operation Vittles This was always going to be a mammoth task. Supplying the two million people of west Berlin meant flying in 2,000 tons of food and fuel a day in summer, and 5,000 tons, including coal, in the winter. It was the most ambitious aerial supply operation in history and would require non- stop, round-the-clock flying into the city's three western airfields.

16. The three major Berlin airfields involved were Tempelhof, in the American Sector, RAF Gatow in the British and Tegel in the French

17. Despite the inevitable hardships, Berliners were firm in their support for the western powers. In September 1948 an estimated 250,000 - one eighth of the western sector's population - demonstrated against Soviet hostility. The symbolism was powerful. In the space of just three years, the Allied forces had switched from the enemy of the German people to their saviour. Stalin stuck to his guns, hoping a traditionally harsh winter would bring the opposition to their knees. But the airlift continued apace. Small, civilian aircraft joined the fleet of military workhorses, delivering flour, meat, vegetables, chocolate, petrol, blankets and medicine.

18. The Berlin sky was animated by a ceaseless procession of air traffic and life carried on against the continual background drone of aircraft engines. Planes touched down every three minutes. The schedule was so tight that each pilot had just one chance to touch down. If the weather or some other factor prevented landing, a pilot had to return to his base and enter the cycle again later.

19. Inevitably there were casualties. In July three American crew were the first killed when their C-47 transporter crashed. In all the operation cost the lives of 65 Germans, British and Americans. By April 1949 the airlift had been running at full throttle for several months and the western powers knew they could hang on indefinitely. The Soviets backed down, entering negotiations and agreeing to lift the blockade on May 5, 1949. In 11 months nearly 300,000 flights had delivered more than 3 million tons of supplies.