Archives have revealed how British intelligence officials used an informal dinner to glean information from Argentine officers (Picture: Getty/iwm.org.uk/Myles Goode)

Two Argentine commanders taken prisoner by British forces after their submarine was severely damaged gave away sensitive information over dinner, newly released files show.

The officers were exhausted and in a state of shock after the ARA Santa Fe was rendered inoperable at the outset of the Falklands War, according to a hitherto secret intelligence document.

British spies circulated information from captains Horacio Bicain, commander of the submarine, and Luis Lagos, leader of Argentina’s troops in South Georgia who were garrisoned in the Grytviken settlement.

They were captured after the Santa Fe was attacked by a British task force at an early phase of the hostilities on April 23, 1982.

Attack helicopter pilots used depth charges, anti-ship missiles and machine gun fire to cripple the vessel — which had provided reinforcements to Grytviken — in one of the first major incidents of the war.

Previously secret files also show how the SAS had its own signals intelligence feed during the operation to retake the Falklands, also known as the Malvinas, after the islands were invaded by Argentina.

After the Santa Fe’s crew surrendered, the British moved in to gain intelligence from the personnel and the vessel itself.

A 1982 photograph of two Royal Marines by the damaged fin of the abandoned Argentine submarine Santa Fe (Picture: Via Mail Online)

An excerpt from a UK intelligence cable following an ‘informal dinner’ at an undisclosed location reads: ‘Both men appeared shocked captain claimed he had been up for 2 days and had not eaten for 36 hours.

‘Effects of quote terrible weather unquote…Both men repeatedly expressed gratitude (and implicity surprise) at humane treatment and the fact that bombardment was not directed at people or buildings.

‘Captain had only been in command for four months (first command) and did not believe Guppy Class would be retained in service after delivery of next 2 German boats on order.’

The Santa Fe sailed on April 13 with marines to reinforce Grytviken, which the Argentines had seized from the British 10 days earlier.

‘They were landed late PM 24 Apr and had made no real attempts at establishing defensive positions thereafter,’ the despatch reads.

‘Bicain claimed he had only light weapons and could not cope with GMPG [General Purpose Machine Gun] armed helos.

‘He had not unpacked his mortars.’

Two commanders taken prisoner after the Santa Fe was severely damaged had dinner with their British counterparts (Picture: Mail on Sunday)

There is no indication as to who attended the dinner on the British side, although the document is signed by ‘BM’, a member of the UK’s 317.9 Carrier Task Force which comprised of Royal Navy ships and elite troops including SAS and SBS contingents.

The dinner is likely to have taken place on a British ship as it is known that Bicain was among Argentinian prisoners transferred to the RFA Tidespring fuel tanker and one of his injured men was taken to lead vessel HMS Antrim.

According to the report, captain Lagos stated he was returning to Argentina when he was ‘surprised’ by the British helicopters and decided not to dive ‘because he could see their torpedoes’.

The intelligence cable released at the National Archives also shows how he had not been expecting to be hit by depth charges in the first known time a helicopter-only attack has taken out a submarine.

The report states: ‘In conversation earlier he admitted that he had had two missions, of which one was Grytviken reinforcement and the other, implicitly although not admitted, was to sink us.’

The signal, which loops in the UK Ministry of Defence and eavesdropping agency GCHQ, also contains details about the pitiful state of the Santa Fe,

The document reads: ‘Submarine in poor condition before attack, dirty, scruffy, haphazardly stowed.’

The Santa Fe’s presence off South Georgia had forced the British task force to withdraw 200 miles from the island after three abortive attempts at landings hampered by icy, blizzard-like conditions.

After being spotted on the surface, the submarine was damaged by depth charges dropped by HMS Antrim’s Wessex helicopter.

Westland Wasp helicopters then struck with AS-12 missiles, with the vessel limping into Grytviken pier where it was abandoned by the crew.

A boarding party found ‘last minute attempts at removing more important material’ in a preliminary inspection of the submarine.

‘Most publications untouched but back rolls, rotors, off-line cypher adjunct to TGN teleprinter and keymat not sighted,’ the report states.

The search took place as the task force completed Operation Paraquet, the codename for the British operation to retake South Georgia in the first UK objective of the war. In the aftermath, an Argentinian crewman, Petty Officer Felix Artuso, was shot dead by a Royal Marine who believed he was about to sabotage the captured submarine.

The crippled sub remained moored just off a small jetty after its seamen were overwhelmed (Picture: Mail on Sunday)

Another was injured by shrapnel from incoming missiles as he fired a machine gun from the submarine at British helicopters before later being evacuated to the Antrim, according to the document.

Fiona Galbraith, of Buckinghamshire New University, a former British Army intelligence officer, said ‘The approach of getting your captured adversaries to relax so they tell their secrets can be found throughout military history.

‘One example is during the Second World War, when the British kept German senior officers in stately homes where they were given the feel of a gentlemen’s club and bugged as they spoke between themselves.

‘In general, the officers of opposing militaries have often found a mutual respect enabling them to speak civilly after an action. There is something of this gentlemen’s code that can be seen in the file about the captured Argentinian officers and continues to survive, even into this cynical era.’

Another piece of correspondence praises GCHQ’s role in the liberation of South Georgia and the Falkland Islands.

Admiral Sir John Fieldhouse, commander of the British surface and submarine task forces, tells then GCHQ director Sir Brian Tovey that the agency provided ‘tremendous service’ with ‘priceless information’.

Sir John wrote: ‘Your staff here at Northwood [military headquarters] are now well integrated into our organisation and are fully earning their keep.’

The records also show how the SAS received a signal intelligence service that was so secret other British ‘eyes’ were not allowed to know they were included in the battlefield updates.

The Falklands War was the first time all branches of the British armed forces had been deployed simultaneously since WW2 (Picture: JDHC Archive/Getty)

Another despatch reads: ‘A special service of Sigint to 22 SAS, Hereford, has been approved and the necessary arrangements for passing relevant information to them have been established.

‘Their requirement is for any information on Argentine orbat [order of battle], deployment, equipment or operations on or around the Falklands.’

Galbraith told Metro.co.uk that the newly opened documents reflect a step-change in the organisation of the various British intelligence channels and overall command structure.

‘The files show how the British in the Falklands War learnt to use multi-source information, including human and technical intelligence, more cohesively,’ she said.

‘During the conflict there was some tension between the Army and Navy about who was in charge which led to the creation of the Permanent Joint Head-Quarters in which all the military branches are represented.

‘Defence Intelligence provides this cohesion and focal point for national and military intelligence agencies supporting overseas military operations.

‘The two main types of intelligence are human intelligence in various formats and technical intelligence, generally signals, which GCHQ does.’

The files are among Falklands War documents opened at the National Archives last month after being kept secret for the past 41 years.

Documents relating to Western intelligence assessments during the US-led invasion of Irag have also been released this year.

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The ‘shocked’ commanders had been trying to sink a British ship, according to a newly-disclosed file.