9. The Argentine Navy suffered its greatest loss on May 2
The Argentine light cruiser ARA General Belgrano was a veteran of World War II, when it had served in the Pacific War as USS Phoenix. By 1982, the old ship was virtually obsolete in every manner, though its weapons could still pose a threat against unarmed auxiliaries. On May 1, the ship was operating outside of the Military Exclusion Zone announced by the British. Both sides had exchanged messages through Swiss emissaries, clarifying their understanding of the exclusion zone. The British had informed their adversary, via the Swiss, that ships inside the exclusion zone were liable to attack by a nuclear submarine, as well as from the surface and air.
HMS Conqueror began trailing General Belgrano on April 30, and notified the Admiralty of its position. The Admiralty informed the War Cabinet and at a meeting on May 1, it was decided to change the announced rules of engagement. Conqueror was ordered to attack and sink General Belgrano regardless of where it was located. Conqueror sank the cruiser on May 2. Nearly half the fatalities sustained by the Argentine armed forces in the war, 323, resulted from the attack. The clear intent of the British task force to expand operations outside of the exclusion zone led to the Argentine Navy withdrawing to its home waters and taking little action in support of the rest of the war.