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Mk 48 torpedo in focus after IRIS Dena sinking by US submarine

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The sinking of the Iranian battleship IRIS Dena by a single Mk 48 torpedo brought renewed focus to the US Navy’s primary submarine weapon, the heavyweight torpedo, which first entered operational service in 1972 and has been continually developed for modern naval warfare.

The attack on IRIS Dena marked the first time since the Second World War that a US submarine used a torpedo to sink an enemy ship.

“In the Indian Ocean, an American submarine sank an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo. A Silent Death,” Secretary of War Pete Hegseth said at a news conference Wednesday.

The Navy says the Mk 48 has long served as the primary undersea weapon and is designed to “defeat all threat surface ships and submarines in all ocean environments.”

Equipment Operator Builder Travis Fryar (right) signals a crane to lower the hook on an inert MK 48 training torpedo during an exploratory ordnance loading exercise at Naval Station Rota, Spain, Jan. 13, 2017, demonstrating the U.S. Navy’s ability to load weapons at nontraditional locations in the U.S. 6th Fleet area of operations. (U.S. Navy Photo: Mass Communications Specialist 1st Class Michael C. Barton/Released)

The Mk 48 is a submarine-launched torpedo that uses information from the launched submarine and its own sensors to locate and attack submarines or surface ships.

Physically, the weapon is built for destructive power. According to Navy specifications, the torpedo is 21 inches in diameter, weighs approximately 3,744 pounds, and carries a 650-pound high-explosive warhead.

According to the Department of the Navy’s fiscal year 2025 budget estimates, a single Mk 48 torpedo costs approximately $4.2 million.

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Sailors are loading torpedoes onto the ship.

Sailors deployed a Mk 48 Advanced Capability torpedo aboard the Los Angeles-class submarine USS Scranton (SSN 756) on June 24, 2021, as part of ongoing U.S. Navy operations in the Indo-Pacific. (U.S. Navy photo by Chief Mass Communications Specialist Josue L. Escobosa/Released)

Lockheed Martin, one of the prime contractors on the Mk 48 torpedo program, says the launch of the torpedo could be guided in real time by cables from the submarine, allowing operators to update targeting information and adjust its course after launch.

If the cable is disconnected, the torpedo can switch to autonomous target acquisition mode, relying on digital guidance systems and onboard signal processing to independently maintain its tracking.

Over time, the torpedo evolved through hardware variants known as “Mods”, each integrating upgraded sensors, guidance and control systems, and propulsion improvements.

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A U.S. service member examines a large torpedo mounted in the submarine's weapons bay while the ship is anchored in Australia.

U.S. Navy officer Devin Simpson checks the MK 48 torpedo aboard the Virginia-class fast attack submarine USS Minnesota during a port visit to HMAS Stirling in Rockingham, Western Australia, Feb. 26, 2025. (Colin Murty/Pool/AFP via Getty Images)

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According to the Fiscal Year 2024 Annual Report prepared by the War Department’s Director of Operational Test and Evaluation, the current fleet includes the Mode 7 configuration developed in partnership with the Royal Australian Navy; Mode 8 is under development and Mode 9 is being pursued as a rapid prototyping effort.

In addition to hardware upgrades, the Mk 48 undergoes recurring software updates known as Advanced Processor Builds, or APBs, which modify tactics, classification algorithms, and operator interfaces to improve performance in increasingly complex subsea environments.