sentences:  The SEAL Delivery Vehicle (SDV) used by the United States Navy SEALs and British Special Boat Service is an example that is in use today.The SDV is used to insert Navy SEALs in shallow coastal waters or attack surface ships 
  
  The Motorised Submersible Canoe, developed by the British Special Operations Executive during World War II, is another example.A wet sub is attractive to the amateur or small commercial builder since many of the problems associated with a dry sub are avoided as only the propulsion and power systems need to be waterproof and life support is much less of an issue than it is with a sealed occupant chamber.