The objectives issued by DARPA are for a vehicle that would have an airborne tactical radius of 1,000 nautical miles, a low-level flight radius of 100 nautical miles (which may leverage surface effects), and a submerged tactical radius of 12 nautical miles. The sum of these must be achieved within eight hours. Endurance on the surface has to be 72 hours in sea states up to five between inserting and extracting personnel. The craft’s payload objective is eight men and their equipment with a total cargo weight of 2,000 pounds.
They obviously want this thing for sneaking commandos into a country off of a sub. As such, it is a waste of money to even try to create such a thing.
Sneaking commandos into a country with a plane flown off of a sub implies truly sending them in with out support (otherwise you could insert them with out needing something that can fly through the air and underwater). This country does not have political courage to send in American soldiers without any hope of support.