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ConflictUS submarine sinks Iranian frigate with Mark 48 torpedo in first submarine kill since WWII
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In March 2026, a U.S. Navy fast-attack submarine sank the Iranian Moudge-class frigate IRIS Dena with a single Mark 48 ADCAP torpedo in the Indian Ocean, marking the first American submarine torpedo kill since World War II. The attack occurred roughly 20 nautical miles south of Sri Lanka as the Dena returned from an international naval review in India. Of approximately 180 crew, 32 were rescued and at least 80 killed. The Mark 48, in service since 1972, detonates beneath a ship's keel to break its hull, and has no reliable defense. The article argues the weapon is critically important for future naval conflicts, particularly in scenarios like a Chinese invasion of Taiwan, where CSIS wargames show undersea dominance is decisive. However, critics note the high cost per round and limited magazine capacity.
Source report
Historic Engagement in the Indian Ocean
In March 2026, a U.S. Navy submarine sank an Iranian frigate with a single Mark 48 torpedo — the first time an American submarine had torpedoed an enemy warship since 1945.
On March 4, 2026, approximately 20 nautical miles south of Sri Lanka in the Indian Ocean, a U.S. Navy fast-attack submarine fired on the Iranian frigate IRIS Dena. Pentagon-released infrared periscope footage showed a massive detonation at the frigate's stern, lifting the ship, breaking its hull, and sending it under.
Defense Secretary Pete Hegseth, alongside Joint Chiefs Chairman Gen. Dan Caine, confirmed the strike, describing it as a "quiet death" and the first sinking of an enemy ship by a torpedo since World War II. Gen. Caine specified that the vessel had been destroyed by a single Mark 48 torpedo.
The Dena, a Moudge-class frigate, was returning from an international naval review in India and transiting international waters when struck. Of roughly 180 sailors aboard, only 32 were rescued; at least 80 were killed. The circumstances — a strike far from the war's center on a ship returning from a diplomatic gathering — drew sharp condemnation from Tehran.
The Weapon: Mark 48 Torpedo
The Mark 48 has been the U.S. Navy's heavyweight submarine torpedo since 1972. In its current Advanced Capability (ADCAP) form, it is the sole submarine-launched torpedo carried by every class of American submarine:
- Virginia-class fast-attack submarines
- Los Angeles-class attack boats
- Ohio-class ballistic-missile submarines (carried for self-defense)
Specifications
| Feature | Detail | |---------|--------| | Diameter | 21 inches | | Length | 19 feet | | Warhead | ~650 pounds | | Guidance | Wire-guided from submarine, or autonomous active/passive acoustic homing | | Capability | Can circle and re-attack if it misses on first pass |
How It Kills
Rather than striking a ship's side like a missile, the Mark 48's warhead is designed to detonate in the water directly beneath the hull. The explosion creates a gas bubble that:
- Lifts the ship's midsection
- Collapses, snapping the keel (the vessel's structural spine)
- Breaks the ship apart
A missile hitting above the waterline can leave a warship damaged but afloat. A torpedo detonating under the keel can break a ship's back and sink it outright — precisely what the IRIS Dena footage showed.
No Reliable Defense
Warships carry layered systems to shoot down incoming missiles and aircraft, but a heavyweight torpedo running deep beneath the surface is extraordinarily difficult to stop.
Why the Undersea Domain Matters
The argument that the Mark 48 is a weapon of the first rank does not rest on one strike against a lightly defended frigate. It rests on where the future of naval warfare is heading — and on what happens when American planners game out the fight everyone worries about most: a Chinese invasion of Taiwan.
When the Center for Strategic and International Studies (CSIS) ran exactly that scenario, playing it twenty-four times across a range of assumptions, one finding stood out: a mon...
[Image: Sailors assigned to the Virginia-class fast-attack submarine USS Minnesota (SSN 783) guide a Mark 48 ADCAP torpedo during a weapons offload onboard Naval Base Guam, Feb. 3, 2025. U.S. Navy photo by Mass Communication Specialist 1st Class Nikita Custer.]
Source
19FortyFiveWestern
Part of this Story
Mark 48 Torpedo Scores First U.S. Submarine Kill Since WWII, Sinking Iranian Frigate