The U.S. Navy amphibious assault ship USS America in 2019 has set sail across the Pacific region with no fewer than 13 U.S. Marine Corps F-35B stealth fighters aboard.

The current cruise represents the latest effort by the Navy and Marines to develop procedures and tactics for operating the Navy’s 10 assault ships as light carriers, each packing more aerial firepower than most of the world’s air forces.

As an earlier proof of concept, USS Wasp in March 2019 deployed to the Pacific region with no fewer than 10 F-35Bs aboard. America in May 2019 forward-deployed to Japan, freeing up Wasp to return to the United States for maintenance.

A Navy assault ship usually embarks just six F-35s or older AV-8B Harrier jump jets plus dozens of helicopters. The vessels can increase their fixed-wing component by reducing the number of helicopters. At a minimum, an assault ships needs just a pair of H-60 helicopters for search and rescue.

With 10 Wasp- and America-assault ships each carrying 20 or more F-35s plus another 10 Nimitz-class supercarriers (and new Ford-class supercarriers under construction), the United States possesses at least 20 aircraft carriers.

By comparison, China in late 2019 is preparing to commission its second flattop capable of carrying fixed-wing planes. The Chinese fleet aims eventually to field six large carriers.

The Royal Navy meanwhile is working up a two-carrier fleet. France, Russia and India each have one carrier. Italy and Spain both operate assault ships carrying Harrier jump jets. Japan and South Korea have announced plans to modify their own assault ships to be compatible with F-35Bs.

The carrier-disparity underscores the sheer size and power of the U.S. fleet.

The idea of a “Lightning carrier” has been years in the making. For years the normal air wing for the Navy's eight Wasp-class assault ships has included around 10 MV-22 tiltrotor transports, four AH-1Z attack helicopters, four UH-1Y light helicopters, five CH-53E heavylift helicopters and just six fighters, plus a couple of Navy H-60s for search and rescue.

But the L-class Wasps were capable of trading helicopters for fighters. During the U.S.-led invasion of Iraq in 2003, four assault ships each embarked up to 20 Harriers in order to contribute to the coalition air campaign.

"This is not the norm for an amphib," Senior Chief Aviation Boatswain's Mate Wynn Young, leading chief petty officer of USS Bonhomme Richard's air department, in 2003 told a Navy reporter. "Our air assets dictate that we operate more like a carrier."

As the Marines began replacing old AV-8Bs and other jets with "fifth-generation" F-35s, planners dusted off the "Harrier carrier" concept and rebranded it as the “Lightning carrier." Other naval experts simply refer to the Harrier and Lightning carriers as "light carriers."

"By 2025, the Marine Corps will operate 185 F-35Bs—enough to equip all seven L-Class ships," the Marines Corps explained in its 2017 aviation strategy. In fact, the Navy expects to operate at least 10 L-class ships, including the Wasps and newer America-class vessels.

An assault ships displaces around 40,000 tons of water, making it slightly less than twice as big by displacement as the Navy's nuclear-powered supercarriers.

A Lightning carrier would embark between 16 and 20 F-35s, compared to the roughly 40 strike fighters that a supercarrier normally carries. An assault ship in the light-carrier role should be able to sustain 40 sorties per day, the Marines estimated. A new Ford-class supercarrier, by contrast, is supposed to be able to sustain 160 sorties per day.

"While the amphibious assault ship will never replace the aircraft carrier, it can be complementary, if employed in imaginative ways," the Corps stated. "A Lightning carrier, taking full advantage of the amphibious assault ship as a sea base, can provide the naval and joint force with significant access, collection and strike capabilities."

And a light carrier could help the Navy shift to a more survivable fleet design. A Ford-class supercarrier costs around $13 billion. An America-class assault ships costs just $3 billion. A light carrier based on an amphibious ship "might be a low-risk, alternative pathway for the Navy to reduce carrier costs if such a variant were procured in greater numbers than the current carrier shipbuilding plan," California think-tank RAND explained in a 2017 report. "Our analysis suggests a two-to-one replacement."

But a supercarrier with its larger size and nuclear powerplant possesses endurance that a conventionally-powered assault ship never could match. Likewise, the bigger supercarriers can embark specialist aircraft such as radar-early-warning planes, radar-jamming planes and tanker drones that are too big for a light carrier to handle.

A light carrier "would not be a viable option for the eventual carrier force unless displaced capabilities were reassigned to new aircraft or platforms in the joint force, which would be costly," RAND pointed out.

The Marines already are planning to equip V-22s with aerial-refueling systems so that the tiltrotors can double as tankers for a Lightning carrier. But no one has proposed a radar-early-warning aircraft or jammer that would be suitable for an assault ship.

A broader compromise could involve the Navy slightly reducing its supercarrier fleet while the fleet more frequently operates assault ships as light carriers with larger numbers of F-35s.

"We might never need to employ this way -- and may not want to, based upon the need to employ our amphibious ships in a more traditional role -- but to not lean forward to develop this capability, to train and exercise with it, is to deny ourselves a force multiplier that highlights the agility and opportunity only the Navy-Marine Corps team can provide," the Marine Corps stated.

David Axe serves as Defense Editor of the National Interest. He is the author of the graphic novels  War Fix, War Is Boring and Machete Squad.