In an earlier blog entry, we discussed the incredible Navy SEAL mini-sub that is the Advanced SEAL Delivery Vehicle or ASDV. While it may not be the most comfortable sub to cruise in, it is already equipped with full life support and an air conditioning system. In stealth operations, this gave them the ability to “swim” long distances under sometimes extreme underwater conditions (which is probably the norm in clandestine missions!) while still being combat-ready when they reach their destinations.

The ASDV was designed as an improvement on an earlier vehicle used by the SEALs, aptly dubbed the “Swimmer Delivery Vehicle” or SDV. It is also known as the SEAL Delivery Vehicle, since the team manning the vehicle is called the SEAL Delivery Team – although its official name still stands as the Swimmer Delivery Vehicle.

This earlier type of manned submersible is flooded, which means that the team riding the vehicle is still traveling exposed to the water, although it is equipped with compressed air that extends the range of each team member’s air tank or rebreather. The team can either use the SDV’s supply of compressed air or rely on each swimmer’s own scuba gear. Aside from life support equipment, the SDV is also equipped with propulsion, navigation and communication equipment, powered by a lithium-ion battery. Like the ASDV, it can deliver Navy SEALs and their equipment to their destination, reconnoiter the area, and return the team to its ship.

The program for designing an SDV started during the Second World War, although its use was not established until 1975. In the area of military operations, however, gathering lessons learned from each mission is key to ensuring future successes, so the SDV was eventually improved to what we now know as the ASDV. There is still one SDV currently in active service in the US military – the Mark 8 Mod 1 SDV.