For long-range missions, SDVs can carry their own onboard compressed air supply to extend the range of a swimmer's own air tank or rebreather equipment. There are two kinds. The "wet" type, where combat swimmers ride on the outside, exposed to the water. Examples of wet SDVs include the American "SEAL Delivery Vehicle". There is also the "dry" type, where swimmers ride in a compartment inside, not exposed to the water. Examples include the American "Advanced SEAL Delivery System". For extended missions on land, a team can be re-supplied by contact with other SDVs.