The sinking of an Iranian warship off the coast of Sri Lanka this week is something a US Navy submarine hasn’t done in more than 80 years and is another indication that Washington’s war with Tehran is taking on a scale and breadth also not seen in decades.
It’s also raising questions as to the broadening scope of the war with Iran.
The Pentagon released periscope video of the attack showing a ship that experienced a massive explosion to its stern as well as what appeared to be still frames showing the ship sinking beneath the waves.
Iranian Foreign Minister Abbas Araghchi identified it as the frigate IRIS Dena, saying it had been lost 2,000 miles from Iran’s shores.
Sri Lanka reported it received a distress signal from the 1,500-ton frigate and dispatched ships and aircraft on a rescue mission. It reported rescuing 32 people, recovering 87 bodies, leaving the rest of the crew missing. Araghchi said there were 130 sailors aboard.
US Defense Secretary Pete Hegseth described the sinking as a “quiet death.”
Araghchi called it “an atrocity.”
The Iranian frigate was reportedly on its way back home after participating in India’s multilateral MILAN 2026 naval exercises, which included ships from what had been described as 18 “friendly foreign countries” and aircraft from three more, including the United States, according to an Indian government website.
A US Navy release said a P-8A Poseidon maritime patrol and reconnaissance aircraft took part, including conducting anti-submarine warfare drills with other participating forces.
But MILAN 2026 was a largely ceremonial event, with videos posted on social media showing members of the Dena’s crew marching in a parade in the port of Visakhapatnam two weeks ago.
Though its presence at the exercise may have been benign, the Dena was one of the newest and most powerful ships in Iran’s fleet, capable of carrying surface-to-air missiles, anti-ship missiles and torpedoes, according to the website shipshub.com.
Analyst Carl Schuster, a former director of the US Pacific Command’s Joint Intelligence Center and a retired US Navy captain, said in the current state of conflict between the US and Iran, the Dena presented a threat.
“Given Iran’s continuing attacks on any US-friendly country it can reach, it is very possible, indeed likely, that the frigate was positioned to strike mercantile shipping either flagged to a US-friendly country or carrying cargo for one,” Schuster told CNN.
“This sinking can be justified as a preventive measure reflecting that concern,” he said.
Alessio Patalano, professor of war and strategy at King’s College London, said the US’ legal justification for sinking the ship can be found in a document signed by President Donald Trump on March 2, which, in part, said the US took action against Iran to ensure the free flow of goods and traffic through the Strait of Hormuz.
The Iranian frigate could be seen as a threat to that flow, Patalano said in a post on X.
But Patalano also pointed out it’s unclear if the Iranian ship was in a state of readiness for war or if the US sub issued any warning of its planned attack.
While neither would preclude an attack on an armed enemy combatant, analysts noted the Iranian ship was not nearly in an equal fight with the US fast-attack sub.
“Submarines confirm a remarkable level of lethality,” Patalano said, adding that it would have been prudent for the Iranian commander to be aware of the active conflict situation his country was in.
“ASW (anti-submarine warfare) should be taken absolutely seriously at one’s peril,” he said.
Some observers Thursday were pointing to parallels between the sinking of the Dena and Britain’s destruction of the Argentinian cruiser ANA General Belgrano during the Falklands War in 1982.
That was the last confirmed time a submarine sank a surface ship, with the Royal Navy attack sub HMS Conqueror striking the Belgrano with two torpedoes and killing 323 Argentine sailors.
That attack was controversial in that it took place outside an initial 200-nautical-mile exclusion zone Britain had declared around the Falklands, and the ship was reportedly heading away from the islands when it was hit.
The Royal Navy maintained the Argentine ship presented a threat to its task force in the South Atlantic. That the ship was moving away has also been disputed.
The exclusion zone Britain did establish around the Falklands in 1982 is illustrative of how that conflict was much more limited in scope than the current hostilities in the Middle East, which, even before the sinking of the Dena, ranged across thousands of miles and involved more than a dozen countries.
Since the US and Israel attacked Iran last Saturday, retaliation by Iran and its proxies has reached as far as Cyprus in the Mediterranean Sea as well as US bases, diplomatic installations and civilian infrastructure in friendly nations around the Persian Gulf.
With the Dena, the theater of combat has now extended well into the eastern edges of the Indian Ocean.
Araghchi, the Iranian foreign minister, warned that Iran would avenge the loss of its prized naval combatant, and hinted that the geographical scope of the conflict may spread even farther.
“Mark my words: The US will come to bitterly regret precedent it has set,” he said on X.
US officials did not say which of the Navy’s 53 nuclear-powered attack submarines was responsible for the sinking as vessel movements are usually closely-guarded secrets within the Pentagon.
But no matter the sub that fired the torpedo, the historical significance is unmistakable.
The last time a US Navy submarine sank an enemy combatant was August 14, 1945, shortly after noon in Japan, when the USS Torsk torpedoed a Japanese frigate, the second of two Imperial Japanese Navy ships it sank that day, according to the Naval History and Heritage Command.
It’s also one of the few times a submarine has sank an enemy ship in battle since that penultimate day of World War II.
Before the Belgrano, a Pakistani sub in 1971 sank an Indian frigate during a conflict between the two South Asian neighbors.
The sinking of the Iranian frigate also brings to mind an earlier battle between US and Iran during 1988’s Operation Praying Mantis.
That confrontation in the Persian Gulf during the Iran-Iraq war came after a US frigate struck an Iranian mine while trying to protect Kuwaiti oil tankers from Iranian attacks.
During a fight with Iranian naval forces, the frigate USS Simpson sank an Iranian gunboat with an anti-ship missile after the Iranian boat fired a missile of its own at the Simpson and two other ships.
It was the first US surface ship battle since World War II and first ship-versus-ship missile duel in US Navy history.
But that US-Iran engagement ended in a day. The current hostilities have been going on almost a week.
US officials can offer no firm end date. Iran is vowing to fight on.
Meanwhile, missiles, drones and now torpedoes are finding new targets.