No, that's false.
The US submarine was not required to personally search for or rescue survivors after torpedoing the IRIS Dena.
In armed conflict, submarines (especially fast-attack types like the Virginia-class) are generally not obligated to conduct on-site search and rescue (SAR) for survivors of a vessel they've sunk, particularly when it's an active military target during hostilities.
Key reasons include:
Practical limitations — A submarine has a small crew (around 130–140), very limited space, no dedicated medical facilities for mass casualties, and no easy way to take on dozens or hundreds of survivors without compromising its stealth, safety, or mission.
Boarding or surfacing to assist would expose it to risk, especially in a war zone.
International humanitarian law (e.g., Geneva Conventions, customary law of naval warfare) requires parties to take feasible measures to search for and collect shipwrecked persons after an engagement, but this duty is qualified:
it applies only if it can be done without undue risk to their own forces or mission.
In practice, for submarines in modern conflicts, this often means transmitting a distress signal (which allows others to respond) rather than direct rescue. Attacking survivors is strictly prohibited, but there's no absolute requirement to expose the sub itself.
Reports from the incident (March 4, 2026) align with this:
The attack occurred in international waters off Sri Lanka.
A distress call was sent (likely from the IRIS Dena itself or automatic systems), prompting Sri Lanka's navy to respond quickly.
Sri Lankan forces rescued 32 survivors, recovered 87 bodies, and continued searching for the remaining ~60–100 (from a crew of ~180), with many presumed dead or missing.
No credible reports indicate the US submarine surfaced, lingered, or conducted its own rescue. US statements (e.g., from Defense Secretary Pete Hegseth) focused on the strike itself, not post-attack SAR.
Some online claims of the US "leaving survivors to drown" appear exaggerated or propagandistic; local/neutral forces (Sri Lanka) handled the response under international maritime SAR conventions (to which Sri Lanka is a signatory).
In short, while the attacking submarine likely reported the incident (enabling others to act), it had no practical or legal duty to perform the rescue itself in this context. The obligation fell to nearby vessels or coastal states like Sri Lanka, which stepped in.