This interesting article appeared on a USN SEALs related blog that I follow. Retired SEAL Michael Wood gives a first-hand account of a close encounter during SDV ops as part of Operation Desert Storm.
One night in October 1983 the almost brand-new Sava class boat Drava ran into serious difficulties in the Adriatic. Unseen by the crew a pin-prick sized hole has developed and the submarine started taking on water. As the water gained, the boat started to slowly sink. 
The Dolphin Class advanced Swimmer Delivery Vehicle (SDV-X) was developed in the 2000s as a US export type based on the SDV Mk.VIII Mod-1 Gator Class SDV in service with the USN SEALs. 
The Piranha was a two-man SDV marketed by The Columbia Group in late 2000s: Read More
In the late 1980s, during the final days of the Cold War, the US Navy SEALs were looking towards a new generation of SEAL Delivery Vehicles (SDVs). One of the advanced designs in circulation was the Closed-Cycle Energy Source (CCES) submersible.
Probably one of the sleekest SDV designs out there; a family of two, four and five-man diver transports developed by MAREX.
Ever fancied burning from Canada to France in 13 hours, under water? 
There are few active submarines as elusive as the Russian 'Special Projects' boat 'Losharik' so this new photo is something of a find! 
Although never built, the German Type-IIIA submarine was to be the first designed with an integral dry deck shelter for smaller vessels. 
The USS Halibut started life as a guided missile submarine performing nuclear deterrent missions at the height of the Cold War. She finished it as one of the world's most secret submarines, performing covert missions close to Soviet shores including Operation IVY BELLS. For these operations she carried a new type of Navy Diver 