To avoid a Czechoslovak membership in NATO, the Soviet Union initiated the largest joint military exercise so far, on the Czechoslovak border on the 10th of August. In the Šumava exercises, which was the name of the manoeuvres, troops from Poland, East Germany, and the Soviet Union participated. At the same time the Soviet Union resumed the criticism of Czechoslovakia, their leaders and their mass media.
Exactly ten days later, at the midnight between the 20th and the 21th August 1968, approximately 200 000 soldiers from the Warsaw Pact, crossed the border to Czechoslovakia. Commando troops and other special forces were airdropped directly into Prague and they seized the airport, which served as a base of operations. By the end of the 21th, almost the whole country was occupied. When the week ended almost 650 000 foreign soldiers were on Czechoslovak soil. It is said that Moscow and the military leadership in Moscow was unsure on how the Czechoslovak military would react - if they would put up a fight and try to defend the country or not. As result of this insecurity the sent dispensable troops into Czechoslovakia were later replaced with regular troops.
The invasion came as a surprise to everyone, even to the Communist Party of Czechoslovakia. The Central Committee broadcasted a message shortly after midnight that they had not known about the invasion. It was also published in the newspapers the next day. Read the message from the Czechoslovak leaders to the people . The Central Committee tried to hold an emergency meeting in a factory outside Prague but it was ineffectual as many of the members were unable to get there and because Dubcek and the other high-ranking members of the government and the Party were arrested shortly after midnight by Spetznatz-troops.
On the 21st the Soviet Union issued an official statement stating that they and the Warsaw Pact countries had acted upon a request of Czechoslovak leaders. They wanted to help with the repulsing of anti-socialistic forces and it was an urgent assistance to the Czechoslovak people. This was true to some extent because a letter was sent to Brezhnev by Alois Indra, Drahomir Kolder, Antonin Kapek, Oldrich Svestka and Vasil Bilak. But none of these were close colleagues of Dubcek. The letter was neither supported by the CC, the Party Presidium or Dubcek himself. Furthermore the statement added: "The further aggravation of the situation in Czechoslovakia affects vital interests of the Soviet Union and other Socialistic states, the interests of the security of states of the Socialist community. The threat to the Socialist system in Czechoslovakia constitutes at the same time a threat to the mainstays of European peace." Read the Pravda Editorial Justifying the Invasion, August 22, 1968
There was no organized resistance to meet the Soviet forces, the military did not receive any orders on defending thecountry and after the initial surprise, the Czechoslovak military was put in house arrest in their barracks. The only resistance the invading forces met were the public's own spontaneous actions, i.e. they blocked bridges, sat themselves in front of the tanks, destroyed and changed direction signs, pretended not knowing how to speak Russian. It is said that the citizens of Prague did not help the forces with anything. When soldiers asked for direction to the Wenceslas Square they pretended not to know where it was, even if it's a famous place that can be conferred with the White House in Washington or the Eiffel Tower in Paris.
Students at the Prague National Radio station put up the most stubborn resistance. They put up barricades of trolleys, buses, trucks and paving stones and used Molotov cocktails to stop the tanks. The invading forces also got some new experiences in urban warfare as the people soon found out that the tanks had their fuel supply above the panzer in the back. People crushed the cistern and put it on fire and with these methods one single unarmed person was able to make a tank useless. Reports state that they were able to hold the radio station until 11 A.M. the 21st of August. The radio broadcasted during these hours and as it was taken and quitted several pirate stations sprung up and broadcasted. Radio-amateurs broadcasted for all they were worth and the military handed out radio-transmitters to the public where it was possible. The 22nd and 23rd there was a rumour spread that the StB was doing massive arrest raids, which was in fact true, thousands of reformists and ordinary people were arrested. But in a short while lists were handed out with the registration numbers of the StB's cars, which often came with arrest orders. On the 24th. three young men were killed by Soviet soldiers as they distributed anti-Soviet leaflets.
What did the rest of the world think about this military intervention? In the UN it was condemned in the Security Council by a vote 10 to 2. But the condemnation never went through as the Soviet Union vetoed the resolution. The Czechoslovak diplomats at UN called the invasion for unlawful and unjustifiable, they moreover pleaded for international support, but got none.
The United States of America ended the secret talks with Brezhnev about the SALT (Strategic Arms Limitation Talks), a meeting that was scheduled in October the same year. The current President Lyndon B. Johnson proclaimed: "The Soviet Union and its allies have invaded a defenceless country to stamp out a resurgence of ordinary human freedom. It is a sad commentary on the Communistic mind that a sign of liberty is deemed a fundamental threat to the security of the Soviet system." [Arms, Thomas, "Cold War Encyclopaedia", New York, 1994, pp. 153] At the same time, Dubcek and his fellow government members were prisoners in Moscow. They were forced to accept several major changes in their policy and in their Party Program. Furthermore, the Soviet Communistic Party received condemnation letters from almost all the Communistic Parties in Western Europe and China.
Upon Dubcek's return to Czechoslovakia, he asked his fellow countrymen to not provoke the soldiers as it may lead to punitive measures against themselves and others. The people should also try to avoid panicking, as it would not help anyone. But the people were also exhorted from other directions that they should do passive resistance and as someone put it: "Not even give them a piece of bread".