To the tens of thousands of people flocking to east London this weekend for the Tall Ships festival, La Esmeralda is just another magnificent ship to admire among the many moored around Canary Wharf.

Almost 400ft long, the four-masted vessel, launched in 1953, is used as a training vessel by the Chilean navy and, for between six and seven months a year, tours the world promoting Chilean interests. But La Dama Blanca, or The White Lady, as she is also known, has a dark history, one that many Chileans want acknowledged if their country is ever to confront its bloody past.

A series of human rights reports, including those by the Inter-American Commission on Human Rights of the Organisation of American States, Amnesty International, the US Senate and the Chilean Truth and Reconciliation Commission, record that in the autumn of 1973 the ship was used to detain and torture victims of the Pinochet regime, who included a British-Chilean priest, Father Michael Woodward.

They detail how the vessel was berthed in the port of Valparaíso, following Augusto Pinochet’s coup d’état. A 1986 US Senate report suggested that as many as 112 people were detained, of whom 40 were women. Rape, the use of electric shocks, mock executions and beatings were reportedly used on the ship. Also on board was Woodward, who, having been tortured onshore, was taken off the vessel for treatment at a naval hospital, but died of his injuries in transit. His remains are allegedly buried in a mass grave under a road.

Claudio Correa, a former Chilean government official who lives in London, was held on the ship with Woodward. He told the Observer that he was transferred from a military academy to La Esmeralda where specialist teams were employed to torture its occupants over several days. “They tortured people with no sentiment,” he said. “They were enjoying it.”

A Facebook campaign has been set up urging people to protest against the vessel’s arrival in London and other European ports. One protester called Carolita explains that its continued use “reaffirms the Chilean navy’s lack of respect for human rights and lack of remorse for actions that have been condemned around the world”, adding that “it is unjust to expect victims to forgive and forget when the perpetrators do not express regret and remorse”.

The site carries testimony from one of the torture victims who recalls how they were constantly beaten: “It was a sight from hell. The red lights. The torturers dressed in party regalia and wearing black masks.”

Perhaps because of its controversial past, the vessel has been a rare visitor to the UK. Last seen in London in 1998, the organisers of the festival have distanced themselves from its arrival.

“Although La Esmeralda is not part of our event, we are very happy that she will also be in London during Sail Royal Greenwich 2015,” says Sjors Mooyman of Sail Greenwich Ltd, the event’s organiser. “This beautiful tall ship is a real addition to the tall ships’ experience. We understand and recognise that this ship may have been used for torture by the Pinochet regime, but we appreciate the ship for its aesthetics and maritime values. We should not judge the ship itself for misuse by a terrible regime in the 1970s.”

But this argument did not satisfy the Chilean exiles protesting outside the vessel yesterday afternoon. They claim that, under international law, including the European Convention on Human Rights, European governments should prevent the vessel from entering their countries’ ports. “We are here to raise awareness of the fact this ship was used as a floating torture centre,” said Carol Concha Bell, whose grandfather was tortured by the Pinochet regime. “We are outraged that this is being promoted as a family day out.” Ana Maria Pelusa, another torture victim said: “We are here because we want the Chilean navy to acknowledge what happened on board Esmeralda and tell us where the victims are. It’s 2015 and these basic questions still haven’t been answered.”

Correa said La Esmeralda should be allowed to visit Britain, providing people were made aware of its history. “It’s OK for it to come here, but it is important to tell the truth about the past. There are a lot of stories that nobody knows.”