Today’s SEAL Delivery Vehicles (SDVs) almost seem like something from a futuristic styled video game. Powered by rechargeable lithium-ion batteries, equipped with state-of-the-art navigation, communication and onboard life sustaining systems the SDV appears as modern day science-fiction; but, these ghost like submersibles have been around since World War II and have served are nations secret wars ever since.

In any type of warfare, secrecy and the element of surprise have always and will always produce the upper hand. When absolute secrecy is required, there is no other element better than water and no better place to get the job done than under it.
The First Spies and Saboteurs Understood This

The Office of Strategic Services Maritime Units (OSS MU) first introduced combatant submersibles referred to as “submersible canoes.” The “Sleeping Beauty” developed by the British and employed by the OSS MU for training was one of the fist and it set the foundation for many advancements to come.

Throughout World War II and beyond the OSS MU continued to design and operate these “Underwater Canoes.” Eventually the program was turned over to the Underwater Demolition Teams where they remained.

Getting In Deep

Traditional submarines are extremely effective in leveraging the principles of stealth, but are limited by their size. Weighing in well over a thousand tons these “whales” require at least 60 feet of water to operate and do not safely work at depths less than 150 feet.

As always there must be something or someone on the tip of the spear to bridge the gap between conventional forces and the enemy. SDVs are an excellent example of this very principle and represent Naval Special Warfare’s ability to bridge these forces at the highest strategic levels.

Leveraging conventional resources including ships, submarines and even parachutes the modern day SDV is designed to be inserted on the fringe of the battle space. Once close to their targets operators would need something much smaller than a submarine, but much larger than a simple SCUBA tank to sustain their biological requirements for extended periods of time.

Insertions can last for upwards of 12 hours putting an incredible amount of stress on ones body. SDVs transcend the gap between human limitations and fantasy as they consistently enable the SEALs operators to appear, from out of no where, anywhere in the world.

Highest Tech

To assist the SEAL operator pilots, SDVs are equipped with the finest Doppler Inertial Navigation Systems (DINS) as well as side and forward looking obstacle avoidance sonar (OAS) suites. Besides these sophisticated navigation systems SDVs are also equipped with a submarine rendezvous and docking systems (RDS) allowing deployed SDVs to make their way back to the safety of their “Mother Ships.” I’ve yet to see a video game that could emulate such a capability but I look forward to the day I do.

Recently Naval Special Warfare has developed a sophisticated “dry” version of an SDV. Still a bulk of them are “free-flooding,” meaning that the inhabitants of the boat are surrounded by water and the associated challenges that come along with being wet for hours upon hours.

Employed by U.S Navy SEAL operators these free-flooding underwater “ghosts” can transport up to 6 combat-equipped operators and an undisclosed amount and variety of payloads. Of course the details are classified, but one could easily speculate the possibility of sneaking agents (human beings) in and out of denied countries around the world.

Old School Invents New School

Prior to 1983, SDVs were actually known as “Swimmer Delivery Vehicles.” Since their inception the now titled SEAL Delivery Vehicles have played an essential, but highly secretive, role in our national security.

SDV missions may include, but are not limited to, small scale direct action missions, top secret reconnaissance and surveillance missions as well as ship and harbor attacks. Because of their size SDVs can also be used to transport, deliver and set up “special packages”.

These special payloads may include large amounts of explosives, technical surveillance equipment or perhaps even, as I speculated before, other human beings.

The SDVs in use today leverage their large cargo compartments to carry demolition devices such as the Mk 4, Mk 5 and Mk 36 charges. Commonly referred to as limpet mines these devices have been designed to be attached to the hull of a ship and can be exploded by time fuse or remote.


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If additional distance is required an SDV can also carry a modified version of the U.S Navy’s Mk 37 torpedo making these underwater vehicles as deadly as they are invisible.

SDVs are perfect platforms to launch both covert and clandestine missions. Consider the utility of such a craft when one either needs to enter a country undetected or has a military or intelligence requirement that would be looked upon unfavorably.

For these reasons, SDVs have been constructed of non-ferrous materials and fiberglass to reduce both their acoustic and magnetic signatures.

I’m sure at some point, if we keep our eyes on the news, we will all have the opportunity to catch a glimpse of one of these boats and the SEALs who operate them as they execute one of their national security missions somewhere on the planet.