A British sub had been detected by the Argentine crew near the Falklands on July 9 and the San Juan had been ordered to reduce its own noise and to monitor it, according a secret report seen by Argentine media.
Sonar experts determined the submarine was a British nuclear ship and three recordings of its presence were sent on to the Argentine army.
The ARA San Juan had been travelling in an area of interest shared by Argentina and the UK and Argentina should have notified the UK before a mission of this kind. However, the Argentine submarine was allegedly ordered by the army not to follow this rule.
Two days before the incident with the British submarine, the ARA San Juan was reportedly in a near-miss incident with a Chinese fishing boat, the Lu Rong Yuan Yu 883, which was on fire.
Another secret report, from November 2016, revealed that the San Juan had problems with its waterproof sealing.
The submarine also had other problems, including losing of 50 litres of oil each day, which affected its hydraulic system.
Before its disappearance, the ARA San Juan only had 14 of the 100 canisters of oxygen it was supposed to carry for emergencies.
Britain and Argentina went to war over the Falklands in 1982, after Argentina invaded and occupied the islands. The conflict lasted 74 days and ended with the Argentine surrender on June 14, 1982, returning the islands to British control.
CREW: The picture highlights the last known whereabouts of the 44 missing submarine crew
https://www.dailystar.co.uk/news/la...arine-monitor-British-nuke-sub-near-Falklands