1. Mid-February 2026 — Iranian ship arrives in India

The Iranian Navy frigate IRIS Dena sailed to Visakhapatnam, India.

It participated in the multinational naval events hosted by the Indian Navy:

MILAN 2026 naval exercise

International Fleet Review 2026.

These events took place roughly 15–25 February 2026 and involved ships from about 70+ countries.

Significance:

This meant the Iranian warship was operating openly alongside many navies, including ships from countries friendly to the U.S.

2. Late February 2026 — Ship departs India

After the exercises ended, IRIS Dena left Visakhapatnam and began sailing westward toward Iran through the Indian Ocean.

At the same time:

A wider U.S.–Iran military confrontation was escalating following strikes on Iranian targets.

3. Early morning, 4 March 2026 — Attack near Sri Lanka

The Iranian frigate was about 40 nautical miles south of Galle, Sri Lanka when it was intercepted.

A U.S. Navy submarine fired a Mark-48 torpedo, striking the ship.

The attack occurred in the early morning hours.

The vessel sent a distress call around 5:00–5:30 a.m. local time reporting an explosion.

Outcome of the strike

The ship sank shortly after the torpedo hit.

Around 180 crew members were believed to be on board.

4. Immediately after the attack — Sri Lanka responds

Because the incident happened inside Sri Lanka’s search-and-rescue maritime zone, Colombo responded.

Rescue operation

The Sri Lanka Navy and Sri Lanka Air Force launched rescue missions.

Search operations took place near Galle.

Survivors and casualties

32 Iranian sailors were rescued by Sri Lankan forces.

At least 87 people were killed, with dozens missing.

Medical care

Survivors were taken to hospitals in southern Sri Lanka for treatment.