Aircraft-carrier decks come in two main types: "ski-jump" and "catapult." In October 2024, an F-35B landed for the first time on the Japan Maritime Self-Defense Force destroyer JS Kaga. Yet Kaga's deck is a "flat deck," unlike a U.S. nuclear carrier or a British carrier. Why do carriers differ so much from country to country? The answer lies in a balance of technology, budget, and strategy.

Why There Are Two Types of Carrier Deck

Launching a fighter from a carrier poses a big problem: the flight deck is far shorter than a land runway, so aircraft struggle to reach enough speed. Two methods were developed to solve this: the "catapult" and the "ski-jump" (an inclined deck).

The catapult type (CATOBAR) uses steam or electromagnetic force to accelerate an aircraft to takeoff speed over a short distance, like flinging a plane from a giant slingshot. Only three nations currently use it: the U.S. Navy's Nimitz- and Ford-class nuclear carriers, France's Charles de Gaulle, and China's newest carrier, the Fujian.

The catapult's biggest advantage is launching heavy aircraft. It can send off the E-2 Hawkeye early-warning aircraft and strike fighters loaded with full fuel and weapons. But developing, building, and maintaining a catapult demands enormous cost and advanced technology. The staggering build cost of the U.S. Navy's newest carrier, the Gerald R. Ford (about $13.5 billion, roughly ¥2 trillion), reflects the complex equipment it carries, including the state-of-the-art electromagnetic catapult (EMALS).

The ski-jump type (STOBAR/STOVL) has an upward-curved lip at the front of the deck. On the same principle as a ski jump, an aircraft's nose points up as it leaves the deck's edge, making it easier to gain lift. Because it uses the aircraft's own engine thrust rather than external force, no complex machinery is needed on the deck, and both build and maintenance costs are far lower.

Many nations' carriers use this method, including the U.K. Royal Navy's Queen Elizabeth class, Russia's Admiral Kuznetsov, China's Liaoning and Shandong, and India's Vikramaditya and Vikrant.

There are drawbacks, though. A ski-jump limits takeoff weight, which can require cutting fuel or weapons. And aircraft with a low thrust-to-weight ratio, such as propeller-driven early-warning planes, cannot fly off a ski-jump alone.

Kaga Is Neither: A Third Option

Here is where Kaga's deck gets interesting. It has neither a catapult nor a ski-jump. Its flight deck is nearly flat, with the bow reshaped from a trapezoid to a rectangle.

That is because Kaga operates the F-35B, a special fighter. The F-35B is a stealth fighter capable of STOVL (short takeoff and vertical landing): it angles its exhaust nozzle downward and uses a lift fan in the middle of the fuselage to land almost vertically. It can also take off after a relatively short deck run, so it needs neither catapult nor ski-jump.

In fact, U.S. Navy and Marine Corps amphibious assault ships (Wasp class, America class) also operate the F-35B from flat decks without a ski-jump. Since these roughly 257-meter ships have a track record of flying the F-35B without one, it was judged that the roughly 248-meter Kaga could do the same.

Why Kaga Didn't Add a Ski-Jump

Technically, a ski-jump would shorten the F-35B's takeoff run and let it launch with heavier weapons and fuel. Indeed, the U.K.'s Queen Elizabeth class pairs a ski-jump with the F-35B and can also use "SRVL" (shipborne rolling vertical landing), gliding onto the deck at an angle while decelerating rather than landing straight down, which lets aircraft bring back more missiles and fuel.

So why didn't Kaga adopt one? There are several reasons.

First, interference with the bow sonar. Kaga (an Izumo-class destroyer) carries anti-submarine sonar below the waterline at the bow. Installing a ski-jump would have meant removing the sonar or making the bow so heavy that it could harm the ship's stability.

Second, controlling refit cost and schedule. Kaga was not newly built but a conversion of an existing ship, so major structural changes had to be avoided to hold down budget and time. Installing a ski-jump would be a large job requiring a redesign of the whole deck.

Third, operational sufficiency. The F-35B is designed as a STOVL aircraft meant for flat-deck operation. With ample operating experience on U.S. amphibious assault ships, it was judged that the lack of a ski-jump posed no practical problem.

The Three F-35 Types and the Carriers That Suit Them

The F-35 comes in three variants, each operated from different ships.

The F-35A (conventional takeoff and landing) is for land bases only, the lightest standard model with the largest fuel tanks. Japan's Air Self-Defense Force deploys it at Misawa and Komatsu bases and plans to acquire 105 in all.

The F-35B (short takeoff and vertical landing) operates from light carriers like Kaga and from flat-deck amphibious assault ships. Its lift fan and vectored engine nozzle allow vertical landing. The Air Self-Defense Force began deploying it at Nyutabaru base in August 2025 and plans to acquire 42 in all.

The F-35C (carrier variant) is exclusive to catapult carriers. Its wings are 45% larger than the A's, giving it better range and payload, but it needs a catapult and arresting wires, so in practice only the U.S. Navy operates it.

In short, a carrier's deck shape is closely tied to the aircraft it carries. Catapult carriers can operate a wide range of types such as the F-35C and early-warning aircraft, while ski-jump and flat decks specialize in STOVL aircraft with thrust-vectoring, like the F-35B.

Each Nation's Carriers: Reading Strategy from the Shape

A carrier's deck shape reveals a country's naval strategy.

The United States boasts the world's only 11-carrier fleet. All are catapult-equipped nuclear carriers operating a wide variety of aircraft, including the E-2D early-warning plane, the F/A-18E/F Super Hornet, and the F-35C. It can deploy a "floating air base" anywhere in the world.

The United Kingdom operates its two Queen Elizabeth-class carriers with a ski-jump and the F-35B. A catapult version was considered but dropped because the electromagnetic catapult was too costly. Using conventional power to hold down cost, it still achieved a large 65,000-ton carrier.

China fields the ski-jump Liaoning and Shandong, but its newest carrier, the Fujian, carries an electromagnetic catapult (EMALS). This ambitious design, a catapult on a conventionally powered ship, suggests China is aiming for a full-scale, U.S.-style carrier.

India operates the Vikramaditya and Vikrant, both with ski-jumps. A shift to a catapult is under consideration for the future INS Vishal (in planning).

Japan's Izumo and Kaga are "light carriers" operating the F-35B from flat decks. Their capacity is said to be about 10 aircraft, short of a full-scale carrier, but a reasonable choice for Japan's defense needs of island defense and air support to remote islands.

How Far Has Kaga's Carrier Conversion Come?

Kaga's refit has proceeded in stages.

The first phase (fiscal 2021–2023) included heat-resistant coating of the flight deck, squaring off the bow shape, and remodeling the air-control room. Because the F-35B's engine exhaust reaches about 1,000°C, the original helicopter deck could not withstand it and needed special heat treatment. The refit cost about ¥23.1 billion (roughly $150 million).

In October 2024, off San Diego, a U.S. Marine Corps F-35B landed on Kaga for the first time and carried out shipboard operational testing.

In August 2025, an F-35B from the British carrier Prince of Wales landed on Kaga for the first time. U.S. F-35Bs also landed, realizing multinational "cross-deck" drills involving Japan, the U.S., and the U.K. Prime Minister Shigeru Ishiba also inspected Kaga and Prince of Wales that month.

The second phase (planned from the end of fiscal 2026) will fit out crew ready-rooms inside the ship and rearrange movement routes for F-35B operations, aiming to complete the refit by fiscal 2028.

In Summary: There's a Reason for the Deck's Shape

A carrier's deck shape is not a mere design difference but the result of a country's technology, budget, and strategic needs. The United States, projecting overwhelming power worldwide, needs catapult-equipped supercarriers; the U.K., wanting to run a relatively large carrier at low cost, finds a ski-jump reasonable. And for Japan, wanting to convert existing helicopter carriers and flexibly deploy air power focused on island defense, the F-35B-and-flat-deck combination is the sensible choice.

In Japan, some welcome Kaga's carrier conversion as strengthening defense, while others worry about consistency with an exclusively defense-oriented policy and about relations with neighboring countries. How is the role of carriers and warships debated in your country? Let us know in the comments.

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