The Peruvian special forces, probably advised, trained and equipped by the SAS, the US Delta Force and the German GSG9, achieved a spectacular success. Surprise was assured because the hostage-takers had become used to a long stand-off, and the moment when they would have expected an armed attack had passed. Such operations also usually take place at night, dusk or dawn. This one took place in mid-afternoon.
The commando force that carried out the strike had rehearsed the rescue. They took over an island near Lima and built a mock-up of the mansion. Television showed footage of commandos in masks training for a raid, blowing a hole in the roof of the replica building, swinging open doors with their weapons ready and sliding down ropes.
The crucial element of the plan was a tunnel dug under the reception hall in the residence, where a number of the guerrillas had begun to play football regularly. That turned out to be their fatal mistake. The tunnel was vital for surveillance, because the ambassador's residence was an isolated building, unlike the Iranian embassy in London, which the SAS stormed in 1980. In Lima the authorities had plans of the building and knew every ventilation shaft, but to insert microphones and cameras they had to get them there, which meant digging a tunnel. The surveillance is believed to have been supervised by FBI experts.
During the four-month siege the Tupac Amaru halted negotiations because, they said, they thought authorities were digging a tunnel. The authorities insisted it was "an invention" . But the guerrillas were right. La Republica said professional miners brought started the tunnel in January, working in shifts. Police played martial music over huge speakers outside the residence to mask the sound of the digging.
The operation was therefore a combination of medieval tunnelling and hi-tech. With surveillance devices in place, the authorities were able to determine exactly where the hostages were kept - and where the hostage- takers congregated.
This and the fact that the hostage-takers had begun playing football on a regular basis gave the authorities an ideal opportunity to strike, immobilising perhaps half the 14 Tupac Amaru. Explosions under the area where the hostage-takers were playing appear to have been quite small - big explosions would have put the hostages at risk - but enough to confuse and disorient the bulk of the Tupac Amaru. Part of the 140-strong special- forces team, which had been hiding in a house behind the residence, then poured through the front gate and blasted open the front door of the residency, while another team attacked from the rear and a third moved up a fire escape on to the roof - the hostages' exit route from the building.
The hostage-takers were probably shot on sight without any attempt being made to capture them. Their main demand had been the release of 400 Tupac Amaru prisoners. The authorities did not want to add any more prisoners to that total, providing motivation for further hostage seizures.
"It was absolutely brilliant" said Richard Clutterbuck, an expert on counter-terrorism. "It was classic in every way. Very good intelligence, very good planning, not rushing it." The hostages were alerted to the imminent rescue - which partly accounts for the smooth evacuation and the loss of only one of 72 hostages.
When a fellow-hostage sidled up to Juan Julio Wicht to warn him they were about to be freed, the Jesuit thought it was just another joke to ease the tension. "I was sitting there and they came up to me and said: 'They're going to free us in a few minutes. Stay calm'," he said yesterday.
"So I thought it was a joke, because we made lots of black jokes." The similarity with other anti-terrorist operations and past Peruvian contacts with the British suggest the SAS and other security experts were involved in planning the operation, though they did not take part directly.
Elite Peruvian police learned how to rescue hostages and kill terrorists during secretive training in the United States at the start of the 126- day standoff, an American instructor said yesterday. Six members of the Hereford-based SAS - four soldiers and two officers - plus three experts from the Metropolitan Police flew to Lima shortly after the hostages were taken. There are reports that secret monitoring, surveillance and signals equipment - including probably microphones and "pinhead" cameras - was flown to Peru as diplomatic baggage. In addition, the RAF flew weapons, stun grenades and explosives to the US. They were then flown on to Peru by the US Delta Force.