Thatcher: Falklands was a war against tyranny
In the radio message recorded for the British Forces Broadcasting Service, she said the battle to reclaim the Falkland Islands was a "just" cause.
She added that the struggle against "tyranny and violence" continued today, and that serving troops could draw "hope and strength" from previous victories.
Lady Thatcher's message has been beamed to the islanders and British troops around the world.
Speaking of the Falklands, Lady Thatcher said: "Aggression was defeated and reversed. The wishes of local people were upheld as paramount. Britain's honour and interests prevailed.
"The whole nation rejoiced at the success; and we should still rejoice."
The broadcast by the 81-year-old former prime minister, who ordered a British taskforce to the south Atlantic after the invasion by Argentina, follows her visit yesterday to an exhibition commemorating the Royal Navy's role in the conflict at the Royal Navy Museum in Portsmouth.