Argentina borrowed money from the UK for some of the equipment it used during the invasion of the Falklands, according to a debt forgiveness group.
The loans, which were completed in 1979, were used to buy two type-42 destroyers and two Lynx helicopters, which were used during the assault on the island.
The debts were never repaid but the UK government is refusing to forgive the debt, which is now the responsibility of UK Export Finance, an arm of the Department for Business.
The Jubilee Debt Campaign said it discovered the information in the National Archives.
"Lending the military junta money to buy British weapons was illegitimate and odious," director Nick Dearden said.
The documents apparently show that labour foreign secretary David Owen signed off on the loans despite being aware of the Falklands issue and potential misuse by the right-wing military junta running the country at the time.