For the last three years, American UAV manufacturers have been trying to sell the Department of Defense on the concept of expendable UAVs, launched from tube like containers carried by aircraft, or special torpedoes launched from submarines. One model, being pushed for aircraft use, weighs less than 20 pounds (after launch), can stay in the air for about an hour, and cruise around at about a hundred kilometers an hour. This model could also be used by submarines, but a larger model (about fifty pounds) has been proposed. This one, based on the current Scan Eagle UAV, could stay in the air several hours, and transmit video back to the high tech "periscope"(actually a float, containing various antennae and sensors), connected to the sub below by a cable).
The problem with these expendable UAVs (that would cost $100,000-400,000 each) is that the pilots and sub crews don't really see a compelling need for them. As neat, and doable, as the technology for them is, the users really don't have any use for them. Warplanes are already in the air, and can see whatever they need to see. Subs have excellent underwater sensors to detect any ships or subs in the area, and an expendable UAV would just help to give their position away.
Meanwhile, the UAV suppliers keep trying to make the sale, because that's what they do.