Two days before the beginning of operation "Danube", the leaders of five Warsaw-Pact countries met in Moscow. Brezhnev informed Ulbricht, Gomulka, Kádár and Zhivkov about the decision made by the CPSU (Communist Party of the Soviet Union) to use military force.

The decision was made partly out of fear, as their Czechoslovak sympathizers would lose their important positions at the upcoming Extraordinary Congresses of the Slovak Communist Party and of the Czechoslovak Communist Party. These sympathizers, led by Vasil Bilak, had written a letter to Brezhnev where they requested military assistance that would put a stop to the approaching counterrevolution. The letter was signed by Vasil Bilak, Drahomir Kolder, Alois Indra, Oldrich Svestka and Antonin Kapek and was, without the knowledge of the Czechoslovak leader, handed over to the Soviet leader during the Bratislava conference on August 3, 1968.

Brezhnev informed the leaders about the letter and suggested that the letter be used as a justification for the upcoming military intervention. And so an editorial was published on August 22 in Pravda justifying the invasion. Phrases like "request" of "assistance through military force" were used.

Circumstances suggest that Brezhnev based his decision of invading on reports he had received from János Kádár and Stepan Chervonenko.

Soviet tanks on their way to Prague

Movie Clip [10 sec]:
Size: 160x120 [221KB]
Size: 320x240 [620KB]

In courtesy of:
Kratky Film Praha a.s

The first-mentioned had insisted on a meeting with Alexander Dubcek where the Bratislava conference was discussed. As Dubcek told the Hungarian leader that his opinion was that the conference had created more unity between the countries, Kádár reminded him that the parties had not changed.
And indeed they had not. Just a couple of hours after the CPSU decision to carry out the invasion, a secret meeting took place between the Czechoslovak President, Ludvík Svoboda, and the Soviet Ambassador in Prague, Stepan Chervonenko. The Ambassador was straightforward about the situation and let Svoboda understand that there will be a military intervention. When Svoboda finally understood the gravity of the situation, he cried out:

"No! Dubcek is not deceiving the CPSU! He is not deceiving the USSR! He's an honest man and a friend of the USSR; you must have faith in him! Have faith in us!"
Navratil, Jaromir. "The Prague Spring 1968". Hungary: Central European Press, 1988, pp. 391.

The Russians met the same negative response from the Czechoslovak people and the rest of the world as they together with the GDR, Poland, Hungary and Bulgaria invaded Czechoslovakia on the night of 20 to 21 August 1968. About a quarter of a million soldiers participated in operation "Danube", which became the biggest armed action in Europe after World War II.

Early in the morning of August 21, transport planes started landing in Prague, at the Ruzyne Airport. Tanks were driven into Prague and soldiers were marching on the streets. The most direct and obvious measure taken by the troops was the arresting and the abduction of Dubcek, Smrkovsky, Cernik, Kriegel, Spacek and Simon.
Read the Report by a Czechoslovak State Security (StB) Official on the Arrest of Dubcek and Other Members of the CPCz CC Presidium, August 21, 1968
Read the The Arrest of the CPCz CC Presidium Members, as Recalled by Josef Smrkovský´s Personal Secretary H. Maxa