The recent sinking of the Iranian warship IRIS Dena by a single Mk 48 torpedo has reignited interest in the U.S. Navy’s most formidable undersea weapon. This heavyweight torpedo, which initially became operational in 1972, has undergone continuous enhancements to meet the demands of contemporary naval warfare.

This incident is particularly significant, as it marks the first use of a torpedo by a U.S. submarine to sink an enemy vessel since World War II. “In the Indian Ocean, an American submarine took down an Iranian warship that believed it was secure in international waters, only to be vanquished by a torpedo,” remarked War Secretary Pete Hegseth during a press conference on Wednesday, capturing the dramatic nature of the event.

The Mk 48 torpedo has long been the Navy’s primary weapon for undersea engagements. It is specifically engineered to “defeat all threat surface ships and submarines in all ocean environments,” according to naval specifications. This capability underscores its critical role in maintaining maritime security.

Illustrating its operational flexibility, a training exercise was conducted on January 13, 2017, at Naval Station Rota in Spain. Equipment Operator Constructionman Travis Fryar was seen directing a crane to lower a hook onto an inert Mk 48 training torpedo. This exercise highlighted the U.S. Navy’s adeptness at loading weapons even at non-traditional locations within the U.S. 6th Fleet area of operations, demonstrating strategic versatility. (U.S. Navy Photo by Mass Communication Specialist 1st Class Michael C. Barton/Released)

The Mk 48 is a sophisticated, submarine-launched torpedo that leverages both the launching submarine’s data and its own onboard sensors to effectively locate and neutralize enemy submarines or surface ships. Its design and capability ensure that it remains a potent tool in the U.S. Navy’s arsenal, adept at addressing threats across various oceanic theaters.

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

Physically, the weapon is built for destructive power. According to Navy specifications, the torpedo measures 21 inches in diameter, weighs about 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.

Sailors position a Mk 48 Advanced Capability torpedo onto 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 Communication Specialist Josue L. Escobosa/Released)

Lockheed Martin, one of the Mk 48 torpedo program’s primary contractors, says it can be guided in real time by wire from the launching submarine, allowing operators to update targeting information and adjust its course after launch. 

If the wire connection is lost, the torpedo can switch to autonomous homing, relying on digital guidance systems and onboard signal processing to continue its pursuit independently.

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

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

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

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 undersea environments.

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