After sinking Iranian ship, did the US military commit a war crime?

That’s one unanswered question that lingers after the announcement Wednesday morning that an as-yet unidentified U.S. Navy submarine torpedoed an Iranian frigate that was far from its home port and had just taken part in multinational exercises hosted by India.

“War Secretary” Pete Hegseth was exultant, underlining its historic significance:

“[Y]esterday in the Indian Ocean, and we'll play it on the screen there,” he said, “an American submarine sunk an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo, quiet death. The first sinking of an enemy ship by a torpedo since World War II.”

Indeed, the strike was lethal. Out of a crew of 180 seamen, only 32 were rescued by the Sri Lankan Navy, which also recovered the bodies of 87 more. The Sri Lankans had received a distress call from the Iranian vessel, the IRIS Dena, apparently shortly after it had been hit by the torpedo.

The frigate was 2,000 miles away from the ongoing US-Israeli campaign against Iran when it was struck and had just participated in India’s multinational Milan 2026 naval exercises in which the U.S. Navy was also represented.

Article 18 of the Second Geneva Convention for the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces at Sea, which was adopted in 1949 and ratified by the U.S. Senate in 1955, states:

"After each engagement, Parties to the conflict shall, without delay, take all possible measures to search for and collect the shipwrecked, wounded and sick, to protect them against pillage and ill-treatment, to ensure their adequate care, and to search for the dead and prevent their being despoiled."

While this provision of international humanitarian law, violation of which constitutes a war crime, applies to submarines as well as to surface ships, there are limited exceptions to this obligation, particularly relevant to submarines.

For example, the relatively limited space on a submarine could make it impossible to accommodate all survivors on board. Nor is a submarine required to take actions that would compromise its safety, such as surfacing within range of enemy forces.

However, in this case, the target of the submarine’s torpedo reportedly sank relatively quickly and may not have even been armed for battle (in part because it was returning from what was essentially a diplomatic mission). And no other Iranian or other hostile ships or warplanes were reported to be anywhere near the attack.

Even assuming for the sake of argument that the American submarine fell under these exceptions, it retained an obligation to do whatever it could to help rescue survivors, if only to alert other ships in the area and/or coastal authorities, such as the Sri Lankan Navy, of the location of the target vessel so that they could render assistance.

But there is no evidence as yet that the submarine, the U.S. Navy, or United State Central Command (CENTCOM) did so. The Sri Lankan authorities indicated Wednesday that they were made aware of the incident by the distress call they received from the ship itself. They didn't even know it was an Iranian ship until they had rescued and communicated with the survivors; the ship had sunk below the surface by the time they arrived on site.

An RS request for comment by CENTCOM regarding compliance with Article 18 emailed Wednesday evening went unanswered as of Thursday evening.

To put the issue in some historical perspective may be instructive.

In the first years of the Second World War, the much-feared German U-boats frequently surfaced to help survivors of their torpedoed targets, providing them with food, water, medical treatment, lifeboats and directions to the nearest landmass.

That practice, however, ended in mid-September 1942 when a German U-boat sank the Laconia, a British troop ship with some 2,700 people aboard, including 1,500 Italian POWs, in the South Atlantic. As other Axis ships approached to aid in the rescue effort, however, the U-boat came under attack by a U.S. Army Air Force bomber, killing dozens of survivors and forcing the submarine to dive. Several days later, the overall German U-boat commander, Admiral Karl Doenitz, issued the so-called “Laconia Order” that forbade future rescue attempts.

The unrestricted submarine warfare that followed -- and that later landed Doenitz on the dock in the Nuremberg trials --helped lay the foundation for the drafting of Article 18 the Second Geneva Convention.

When Secretary Hegspeth asserted during his triumphant briefing Wednesday, "Our rules of engagement are bold, precise and designed to unleash American power, not shackle it," is this what he had in mind?

“I can't assess whether the U.S. undertook ‘all possible measures’ to search for and collect the shipwrecked without having a better idea of what was possible in this situation,” wrote Brian Finucane, a senior adviser specializing in military affairs with the U.S. Program at the International Crisis Group, in an email to RS. “But I certainly think the U.S. military needs to explain itself, particularly if no attempts at search and rescue were made.”