Swimmer Delivery Vehicle (SDV): Submarines have operated with special operations teams since the days of WWII with Underwater Demolition Teams (UDT), commonly known as "SEALs" (Sea-Air-Land) are used in a variety of clandestine operations. Carried in a special watertight tank "piggybacked" to a submarine, the SDV gives the SEAL team a greater range of stealth, mobility and endurance.
Sea - Military - Submarines
During World War II, the Italian "Maiale" was used to transport frogmen into a harbor or anchorage occupied by enemy ships. When close to an intended target, the frogmen would exit the Maiale, place a mine on the ship's hull, set a timer, return to their mini-sub, and move away from the target, clear of the explosion. Maiale class submarines were used with great effectiveness against British ships anchored in Gibraltar.