On 17 February, the Indian Navy posted a cheerful message on X.
"Welcome!" it wrote, greeting the Iranian warship Iris Dena as it steamed into the port of Visakhapatnam to join an international naval gathering.
Photographs showed sailors in crisp whites and a grey frigate gliding in the sea harbour on a clear day. The hashtags spoke of "Bridges of Friendship" and "United Through Oceans".
Two weeks later the ship, carrying 130 sailors, lay at the bottom of the Indian Ocean. It had been torpedoed by a US submarine off Sri Lanka's southern coast on 4 March.
Commissioned in 2021, the Dena was a relatively new vessel - a Moudge-class frigate of Iran's Southern Fleet, which patrols the Strait of Hormuz and the Gulf of Oman.
