With the British bombing raids in progress over the Falklands the war spread from the air to the sea.
Unless peace talks provided a surprise breakthrough soon significant loss of life was imminent.
The success or failure of the British task force depended on its two aircraft carriers, Hermes and Invincible.
It was with this in mind that Mrs Thatcher made the most controversial decision of the war. She gave her permission for the nuclear submarine HMS Conqueror to sink the Argentine cruiser the General Belgrano.
To Mrs Thatcher and her war cabinet the fact that the ship was a veteran of World War II and was outside the exclusion zone was irrelevant. It carried exocet missiles and therefore posed a potentially fatal threat to British ships.
Three-hundred-and-sixty-eight men were killed as the cruiser sank.
Defending her decision to MPs she said: "Had we left it any later it would have been too late."
Within days the Royal Navy was too to feel a profound shock as it took its first casualties.
HMS Sheffield, a modern destroyer, was hit by a single exocet missile. Despite its failure to explode the airbourne missile drove a massive hole in the ship's side and within seconds the ship was covered in thick acrid smoke. Twenty-two men were killed and the ship was completely disabled and later sank.