Belgrano posed a real threat to fleet

To the casual onlooker it may have seemed as provocative as The Sun's famous 'Gotcha' headline, but when HMS Conqueror slipped into Faslane naval base flying the Jolly Roger she was simply upholding a fine old tradition.

Royal Navy submarine crews had raised the 'skull and crossbones' when returning home from successful patrols since the First World War.

In 1982, however, angry critics regarded the nuclear-powered boat – and her political masters – as criminally culpable as the pirates who had flown the flag while plundering the high seas centuries earlier.

No single event in the Falklands war provoked a greater storm of controversy, or caused greater loss of life, than Conqueror's sinking of the General Belgrano.

Opponents of the attack say the Argentine cruiser was outside the 200-mile exclusion zone imposed by Britain around the islands and that the elderly warship was steaming away from them.

Supporters point out that it only takes moments for a ship to change course and that the former US Navy vessel posed a very real threat to British forces.

Some facts are irrefutable. At supper time on May 2, the Churchill-class hunter-killer submarine under Commander Chris Wreford-Brown fired three torpedoes. Two of them hit their target and exploded.

The 12,000-ton ship rolled over and sank within an hour, leaving around 290 crew members dead and 30 or so more dying of burns and exposure as they took to their liferafts in the icy waters of the south Atlantic.

It was the first time that a nuclear submarine had fired torpedoes in anger and the first time a ship had been sunk in this way since the Second World War.

In her former guise as the USS Phoenix, the light cruiser had already survived the Japanese attack on Pearl Harbour 40 years previously.

Under her new owners, the Belgrano was steaming 50 miles east of Los Estados, the easternmost tip of Argentina, when Conqueror first made sonar contact on April 30, 1982.

Wreford-Brown followed the bearing and sighted the ship, bristling with 15 long-range six-inch guns and anti-aircraft weapons, late the next morning. Accompanying her were two destroyers armed with sea-skimming Exocet missiles.

With the Argentine carrier Veinticinco de Mayo to the north, task force Rear-Admiral Sandy Woodward decided that he was in danger of being caught in a pincer movement.

He feared Belgrano might try to shake off her pursuer by crossing the Burdwood Bank, a patch of shallow water 200 miles long and 70 miles wide, before heading straight for Hermes and Invincible.

Margaret Thatcher's war cabinet gave the go-ahead for the attack and by 6.30pm on May 2 the cruiser was a large slab of grey in Conqueror's periscope.

After shouting the bearing and range – 1,480 yards – Wreford-Brown gave the order to shoot.

He wrote later: 'I distinctly recall seeing an orange fireball in line with the main mast, and shortly after the second explosion I thought I saw a spout of water, smoke and debris from forward.'

The destroyers launched depth charges but quickly lost the submarine's scent as she fled the scene. A third of Belgrano's 1,000-strong crew perished.

Commander Jeff Tall, who was Woodward's submarines staff officer in Hermes and now runs the Submarine Museum in Gosport, is convinced it was a job that had to be done. He said: 'The Argentinians have since said Belgrano was a legitimate target, that they would have done the same thing. She was part of an aggressive act by the Argentinians.'

In an emotional TV interview a year later, Mrs Thatcher said: 'I think it could only be in Britain that a prime minister was accused of sinking an enemy ship that was a danger to our navy, when my main motive was to protect the boys in our navy.'

Wreford-Brown himself said of the attack: 'The Royal Navy spent 13 years preparing me for such an occasion. It would have been regarded as extremely dreary if I had fouled it up.'So proud at sub's magnificent effort

Today any budding submarine skipper can track banana boats and cross-Channel ferries through the periscopes that HMS Conqueror's captain used to sink the Belgrano.

The Royal Navy Submarine Museum in Gosport has two optics from the nuclear-powered boat on display – a binocular 'scope for general surveillance and the monocular type used in the attack.

Commander Jeff Tall, the museum's director, hopes that when visitors peer through them at the ships in Portsmouth harbour, they will 'do it with pride.'

The retired officer was a Cold War submarine commander and a staff officer on board HMS Hermes during the Falklands conflict.

And he bristles, more from frustration than anger, when anyone suggests that the destruction of the Argentine cruiser could have been avoided.

He said: 'The Argentinians were told quite clearly that if they left harbour showing hostile intent, then Her Majesty's Government would take whatever action they saw fit to ensure the safety of the task force.'

Cdr Tall points out that the Exocet-equipped Belgrano was the southern element of a pincer movement designed to trap the British task force. Although she had been steaming away when she was sunk, like any ship she could have turned around in an instant.

'We had three potential Exocet-firing groups against us – the aircraft carrier Veinticinco de Mayo to the north, three Type 69 frigates out to the west and Belgrano south.

'They could have mounted that kind of operation against us at any time. The simple truth was, action had to be taken to keep us safe. Whether they were east, west, north or south or steaming round in circles didn't really matter. They were a threat. We couldn't operate safely with them there.

'We were lucky that we had our assets in the right place at the right time.'

Asked how he felt about the loss of life, Cdr Tall said: 'They'd come out to kill us. They weren't just carrying stores from A to B. The scenario would have been aircraft attack to soften us up, then attack with the Exocets.

'The scale of the loss of life was deeply hurtful. I didn't want young men to lose their lives. But the important thing is, the Belgrano was an ancient ship. It should never have been at sea.

'It certainly shouldn't have been sailing in a straight line taking no anti-submarine precautions. They were naive.

'Northwood (the operational command centre in London) couldn't believe the Argentinians ignored our warnings. They took a chance. They knew we had nuclear-powered submarines down there. They've since acknowledged they got it wrong.'

Cdr Tall said Conqueror's mission is a landmark in the annals of naval warfare.

'It demonstrated the real power of the nuclear-powered attack submarine. It's the first time in history that a submarine action has had a direct effect on the outcome of a conflict, because it put their navy back in harbour, never to emerge.

'It was a magnificent effort. I look back on it with pride.'