On the morning of November 4 1979, a stream of buses carrying young Iranian students joined a crowd of thousands demonstrating outside the walls of the US Embassy compound.

For days, vigorous anti-American protests had run through Tehran after the US offered refuge to the Shah of Iran, Reza Pahlavi, who had fled the country eight months earlier as the Iranian Revolution swept him from power.

And on November 4 around 300 radical students, calling themselves Imam's Disciples in reverence to Ayatollah Khomeini, the de facto ruler of the new Iran, decided to storm the Embassy and stage a sit-in.

The students were mainly from a group called the "Office for Strengthening of Unity Between Universities and Theological Seminaries" or the OSU, a dynamic force in the Iranian Revolution and reshaping of Iran after decades of corruption.

Swarming over the walls and climbing the gates, the students poured into the acres of grounds of the Embassy in central Tehran, rounding up 66 American hostages - men, women, Marines, consular staff, whoever they could find.

Outside the crowd burned the stars and stripes and shouted "Die America". In the confusion, some Americans managed to slip away from the students and even Ayatollah Khomeini asked the radicals to leave the Embassy. Within days, 13 Americans - the female and black hostages - were released.

But soon the sit-in hardened into a siege, the hostages were paraded blindfolded before the world's television cameras and President Jimmy Carter found himself facing a humiliating crisis that would last 444 days and never leave him.

Sensing the frustration of Mr Carter, who was reminded of his impotence by nightly news broadcasts solely dedicated to the ongoing drama, Ayatollah Khomeini became determined to transform the hostage crisis into a victory over the "Great Satan" of America.

"This has united our people. Our opponents dare not act against us," said Ayatollah Khomeini, who led his country's demands for the return of the Shah to face trial in Iran.

For months the crisis persisted. America and Iran cut off diplomatic relations and Mr Carter suspended trade with Iran. The safety of the 52 hostages, who were moved out of the Embassy, imprisoned, and then returned to the mission, hung over the start of the presidential election campaign of 1980.

In April, five months into the stand-off, Mr Carter ordered an ambitious rescue mission, launching helicopters from secret bases in the Middle East and the aircraft carrier USS Nimitz in the Indian Ocean. But the mission was a disaster.

Two helicopters collided in the Iranian desert, killing eight American servicemen. Apparently, the planners of the operation had not considered the possibility of a sandstorm.

Mr Carter suffered increasing criticism through the summer of 1980 as the election campaign tightened. Ronald Reagan, the Republican candidate, and his running mate, George W. Bush Snr, the former director of the CIA, accused him of plotting an "October Surprise" to spring the hostages to freedom on the eve of the election.

In the end, there was no surprise, only slow and bitter bargaining. Ayatollah Khomeini softened his stance as Iran stumbled into the Iran-Iraq war, short of money, curtailed by sanctions and aware that President Reagan, due to take office in January 1981, would never negotiate.

The American hostages were released on January 21 1981, Mr Carter's last day in office. A deal negotiated through the Algerian Government released $8 billion of Iranian funds frozen in bank accounts across the world. The hostages flew to Germany, and then home.

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