Lockheed Martin
Lockheed Martin's design is loosely based on its RQ-170 Sentinel and the overall design does not appear much different from Lockheed Martin's UCLASS offer, the Sea Ghost. That drone was supposed to feature stealth technology to help it conduct strike and ISR missions.
But when the Pentagon shifted the program to aerial refueling, the stealth requirements were dropped. Despite this, Lockheed Martin has decided to keep its flying wing design.
A flying wing design is aerodynamically efficient because it requires less thrust and fuel to fly, and its spot factor is small when its wingtips are folded up.
A flying wing design for a tanker also has the added benefit of having more space than conventional designs, which allows it to carry more fuel. The Navy wants its new drone to be able to hold over 14,000 lbs of fuel.
From a mechanical standpoint, flying wing aircraft are considered slightly easier to maintain as well because they tend to have a lower number of parts.
The drone will also be equipped with sensors and cameras that enable it to carry out limited ISR missions.
Boeing
Boeing's design is based on its Phantom Ray stealth UAV demonstrator. Boeing has the most experience in aerial refueling, as well as naval aviation as a whole — the F/A-18 Super Hornet and the EA-18G Growler dominate the current naval air fleet.
Like Lockheed Martin's design, the drone has a massive fuel tank, meaning it will have no difficulty meeting the Navy's 14,000lbs of fuel and 500 nautical mile range requirements.
Boeing's design is the only one that has a working prototype, though it has not yet flown. The drone has been tested in St. Louis on Lambert Field.
The drone was operating on a painted outline of an aircraft carrier flight deck to test if it could function well in the limited space.
Deborah VanNierop, a spokeswoman for Boeing, said that they had "successfully controlled the aircraft through all of the most challenging flight deck scenarios, including day and night operations," in tests that were "designed to show how the aircraft can be taxied and operated within the tight confines of the carrier flight deck."
Boeing's candidate was also adapted from the original UCLASS program.
General Atomics
General Atomics' design is based on their Sea Avenger, a carrier-based version of their Avenger UAV, a strike aircraft that was intended to succeed its MQ-9 Reaper.
The Sea Avenger was re-adapted for refueling operations after the Pentagon cancelled the UCLASS program.
General Atomics and Boeing are working on the proposal together, and this drone would be among the largest projects General Atomics has pursued.
The drone will be equipped with electromagnetic technology that will enable it to fit in seamlessly with the Electromagnetic Aircraft Launch System on board Ford-class carriers.
It will also be powered by the Pratt & Whitney Canada PW815 turbofan engines, one of the most efficient and modern engines currently used.
The design is still heavily based on the Avenger, which was designed for strike and ISR missions.
The company has already announced that it will not build a flyable prototype, choosing instead to use its Avenger prototypes for things like ground tests. General Atomics provides the US military with more drones than any other company.