In early March 2026, a small but interesting footnote in submarine history occurred.

On 4 March 2026, periscope footage from the Improved Los Angeles-class fast attack submarine USS Charlotte (SSN-766) was released showing her torpedoing the Iranian Moudge-class frigate IRIS Dena the previous day. The Iranian frigate was returning from a naval review in India and was in international waters south of Sri Lanka when a Mk. 48 torpedo sank it. Footage clearly shows the torpedo detonating under the stern of the vessel, lifting it out of the water, and breaking the stern off. The vessel then sank stern first. Sri Lankan authorities, responding to the sinking, reported that, of the estimated 180 on board, 32 survivors were rescued and an additional 87 bodies were accounted for.1

USS Charlotte (SSN-766) in Yokosuka, Japan, on 24 November 2015.2
A Mk. 48 torpedo on display in USS Blueback. This torpedo is similar to the one fired by USS Charlotte, but an older variant.
IRIS Deylaman, a Moudge-class frigate like IRIS Dena. While Iran technically classifies these ships as destroyers, based on their size and armament, most other nations classify them as either corvettes or frigates.
Screen capture from a video of a Mk. 48 torpedo detonating under the stern of the Iranian frigate IRIS Dena on 3 March 2026.

What’s interesting is that, according to statements from U.S. officials, Charlotte actually fired two torpedoes, but the first one missed.3 This does raise questions about the submarine’s position and circumstances at the time of firing, since they appear to be broadside of the target and were close enough to get a good optical view through the periscope. Did they have time to get into a favorable position and perform Target Motion Analysis (TMA), or did they simply snapshot off a couple of torpedoes? Given what we know about the Mk. 48 torpedoes, why did the first torpedo miss? Were they or weren’t they using wire-guidance? If they were using a wire, did it break or was it cut? Additionally, what mod of Mk. 48 was it? We could speculate all day, but I’ll stop there.

After discussing this event with my colleagues on USS Blueback, we agreed that, since the torpedo detonated under the stern of the vessel, it was likely in passive acoustic homing mode. So the torpedo was homing in on the sound of the screws. The periscope footage also shows the submarine relatively close to the target, though it’s clearly magnified. I mistakenly thought this footage was originally from a modern photonics mast (like on a Virginia-class boat), given that it looks like an infrared image, but since this was a Los Angeles-class submarine, the periscope footage was likely taken with her Type 18 search periscope. This particular scope, while optical, has photo/video recording, low-light enhancement, and IR imaging capabilities. The periscope’s image can be displayed on a screen in the control room. (The other periscope, a Type 2 attack periscope, is also optical, but doesn’t have low-light or any image enhancement capabilities.)

(left) A Type 2 attack periscope. (This is also what USS Blueback currently has.) (right) A Type 18 search periscope.

This event is also significant because, to my knowledge, it’s the first time Mk. 48 torpedoes have been used in combat (as opposed to in a SINKEX), and it’s also the first time in over 80 years that a U.S. Navy submarine has fired a torpedo in anger. The last time was on 14 August 1945, when USS Torsk sank several ships in the Sea of Japan just before the end of World War II.

Notes

  1. Uditha Jayasinghe et al., “U.S. Sub Sinks Iranian Warship off Sri Lanka, Killing 87 and Expanding War Zone,” Asia Pacific, Reuters, March 4, 2026, https://www.reuters.com/world/asia-pacific/sri-lanka-rescues-30-people-board-distressed-iranian-ship-foreign-minister-says-2026-03-04/. ↩︎
  2. U.S. Navy photo by Petty Officer 2nd Class Brian Reynolds. ↩︎
  3. James LaPorta and Eleanor Watson, “Torpedo That Struck Iranian Warship Was Fired by USS Charlotte, U.S. Officials Say,” CBS News, March 5, 2026, https://www.cbsnews.com/live-updates/us-iran-war-spreads-azerbaijan-israel-strikes-tehran-lebanon/. ↩︎

Bibliography

Jayasinghe, Uditha, Idrees Ali, Phil Stewart, Idrees Ali, and Phil Stewart. “U.S. Sub Sinks Iranian Warship off Sri Lanka, Killing 87 and Expanding War Zone.” Asia Pacific. Reuters, March 4, 2026. https://www.reuters.com/world/asia-pacific/sri-lanka-rescues-30-people-board-distressed-iranian-ship-foreign-minister-says-2026-03-04/.

LaPorta, James, and Eleanor Watson. “Torpedo That Struck Iranian Warship Was Fired by USS Charlotte, U.S. Officials Say.” CBS News, March 5, 2026. https://www.cbsnews.com/live-updates/us-iran-war-spreads-azerbaijan-israel-strikes-tehran-lebanon/.