Mark 9 SDV: The SEALs’ mini-sub that packed full-sized torpedoes

Most people have heard of the Navy SEALs, the maritime component of the U.S. Special Operations Command (SOCOM). They were the ones who conducted the raid that killed Osama bin Laden, the leader of al-Qaeda, in 2011, in addition to conducting several other high- and low-profile raids and hostage rescues in the past 20 years. But not many people have heard about the SEAL Delivery Vehicle (SDV) Teams; a small community of SEALs within the already small community that is Naval Special Warfare.

The Navy SEAL Delivery Vehicle Teams primarily specialize in underwater insertion and extraction of special operations forces, underwater direct action, and underwater special reconnaissance.

The concept of the frogman, a commando specializing in underwater special operations, really came into life during World War II. First, the Italians and then the British developed and deployed frogmen to great effect, sinking or damaging several enemy vessels throughout the conflict.

Established in the 1980s, the SDV Teams have used several underwater vehicles for their operations. The vast majority of SDVs were transporters, designed to carry SEAL operators and munitions closer to a target without alerting the enemy. Several iterations of the Mark 8 SDV, which is still in service, made up the SDV Teams’ fleet for decades. Now, Naval Special Warfare Command is upgrading its fleet of mini-submarines with the introduction of the Mark 11 Shallow Water Combat Submersible (SWCS) and the Dry Combat Submersible (DCS).

But there was an additional, far deadlier SDV that served for years. Its mission came straight out of a Tom Clancy novel.

MARK 9: A unique SDV

The now-decommissioned Mark 9 SDV; for years it was the most lethal SEAL Delivery Vehicle in Naval Special Warfare’s arsenal. (Navy SEAL Museum)

Unlike its brethren, the Mark 9 SDV was primarily designed for offensive operations.

The mini-submarine was designed primarily for hydrographic reconnaissance, anti-submarine, and anti-ship operations. Its ability to cruise clandestinely made it an ideal platform for special operations inside enemy harbors or anchorages.

Operated by two fully geared SDV SEALs (usually one officer and one enlisted troop), the Mark 9 could carry a number of underwater munitions that could sink enemy vessels. The two operators, a pilot and navigator, were located at the front of the Mark 9. They would lie prone side-by-side on the front of the vehicle.

Right behind them was a large cargo area that could hold several different munitions, including limpet mines, satchel demolition charges, and, more importantly, the Standoff Weapon System. Designed specifically for the Mark 9 SDV, the Standoff Weapon Systems was a modified Mark 37 submarine torpedo that could be used against enemy vessels from a distance, as opposed to the limpet munitions which had to be physically attached to a target. However, the Standoff Weapon System required the Mark 9 SDV to be within sight of the target.

Related: SWCC are the Naval Special Warfare’s elite boat operators

The Mark 37 torpedo has a maximum range of 13 miles and carries a 330-pound HBX-3 high explosive warhead. (Wikimedia Commons)

The Mark 9 SDV was propelled by two electric motors that used rechargeable batteries, allowing for stealth and endurance. It also sported a navigation system (the Doppler Inertial Navigation System), sonars (on the sides and front) that could detect obstacles, and a special navigational device that was used to find the mother submarine and dock in its dry dock shelter successfully and safely.

The Mark 9 (Mk 9), Mod 0 SEAL Delivery Vehicle is one of the few mini-submarines developed for offensive operations against surface vessels and submarines. Its low-profile make that resembles a Sole fish also made it harder to detect and a bit more agile. The Mark 9 SDV could easily sneak into an enemy harbor, strike against an enemy ship, and slither away into the cold darkness of the ocean. Its characteristics and ability to cruise clandestinely made it an ideal platform for attacks inside enemy harbors or anchorages and strategic reconnaissance in littoral or shallow waters.

Like the Mark 8 and Mark 11, its less-deadly counterparts, the Mark 9 SDV was flooded, meaning that the two SEAL operators were exposed to the water and had to either use the machine’s air supply or activate their Drager breathing apparatuses, which emit no bubbles, once closer to the target.

The SDV could be deployed from the sea, underwater from a submarine, or from the surface, land, or even by air via a helicopter.

By the late 1980s, however, the Mark 9 was decommissioned because the Mark 8 could perform all of its missions, except deploying the Standoff Weapon System, and the Naval Special Warfare Command sought to save money and manpower.

SDVs: An invaluable capability few countries possess

Members of SEAL Delivery Vehicle Team Two (SDVT-2) prepare to launch one of the team’s SEAL Delivery Vehicles (SDV) from the back of the Los Angeles-class attack submarine USS Philadelphia (SSN 690) on a training exercise. (U.S. Navy photo by Chief Photographer’s Mate Andrew McKaskle)

The SDV capability is a unique arrow in the U.S. military’s quiver. Through its inherent stealth, the capability enables clandestine and covert missions that would otherwise be off-limits. Both the military and the intelligence community can find the SDV capability useful.

In the era of Great Power Competition with near-peer states like China and Russia, the SDV capability becomes ever more useful. Both Beijing and Moscow have been using innovative ways to counter conventional U.S. military capabilities

For example, China has been fortifying the illegal man-made islands in the South China Sea with Anti-Access/Area Denial (A2/AD) weapon systems as a way to prevent the U.S. Navy from deploying in the area in force. What that means is that if there is a conflict in the area, U.S. aircraft carriers won’t be able to reach the islands to deploy their aircraft, thereby rendering one of the U.S. military’s most potent weapons impotent.

Related: What do we know about China’s new ‘6th gen’ fighters?

An example of China’s Anti-Access/Area Denial (A2/AD) defenses. (Office of Naval Intelligence)

The situation is becoming similar in the Russian area of operations. After invading and annexing Crimea, Moscow has been fortifying the peninsula with Anti-Access/Area Denial (A2/AD) systems to prevent its retaking by Ukraine with the support of the West in a potential full-blown conflict. U.S. warships won’t be able to get near the area to be as effective as they could be.

That’s where the SDV capability comes in. Special operations units carried by SDVs close to the self-made Chinese islands in the South China Sea or the Crimea can target and destroy the emplaced defensive systems, allowing larger conventional forces to leverage their capabilities in full.

Editor’s Note: This article was originally published in September 2021.

Feature Image: Navy SEALs securing a Standoff Weapon System on a Mark 9 SDV before a mission. (Wikimedia Commons)

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