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For many, the pricetag of the F-35 has been its Achilles heel. With the program’s total cost now at a baffling $1.7 trillion, the Lightning II easily cleared the bar to become the most expensive airplane program in history. That’s not only concerned U.S. taxpayers, but international customers, as tariff rates have scared away some foreign militaries hoping to buy the jet.

Regardless, 19 nations have thrown their hat in the ring, with over 1,000 F-35s delivered around the globe. And while the development cost might sound absurd, it starts to make sense when you realize that it isn’t just for creating one jet, but for three.

The winner of the Joint Strike Fighter competition, Lockheed Martin was contracted to build a fifth-generation fighter that could replace four aging aircraft across three branches of America’s military. The result is three planes that, despite appearing identical on the surface, only share about 20% of their components beneath their radar-absorbent skin.

But what makes each one unique? Let’s take a look at the three versions of the F-35 and the roles they play for today’s militaries. Time to brush up on our ABCs.

A is for Air Force

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First entering service in 2016, the F-35A was drawn up primarily as a replacement for Lockheed’s F-16 Fighting Falcon, as well as the iconic A-10 Thunderbolt II. Considered the base-model Lightning II, the F-35A is the conventional takeoff and landing variant, flying from standard runways and bases. It doesn’t need to carry the complex systems its two brothers require, making it the smallest, lightest, and fastest variant of the three, able to handle maneuvers up to 9 g’s.

The F-35A is also the only one of the trio to have an internally stored gun. While all three variants can carry the Gau-22/A, the F-35A has its 25mm cannon stored on the left of the fuselage rather than in an external gun pod on its belly. Since the U.S. Air Force uses a boom refueling system, it’s also the only version to feature a refueling port, located on top of its fuselage. Both the B and C feature a probe for drogue refueling.

The F-35A is also the base for Israel’s F-35I. Using an F-35A’s airframe and hardware, the “Adir” (Hebrew for “mighty,” inspired by the biblical Book of Psalms) features Israeli-made electronic warfare systems and countermeasures, as well as the flexibility to integrate and deploy bombs and missiles.

B is for Britain

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In 1967, British firm Hawker Siddeley introduced one of the most unusual aircraft to ever fly, the Harrier. A ground-attack aircraft with short vertical take-off and landing (SVTOL) capabilities, it was a fighter that could operate anywhere a helicopter could. The pride of British engineering, the Harrier was the backbone of the Royal Air Force during the Falklands War and served well into the 21st century. And American Marines began flying a modified “AV-8B Harrier II” in 1981.

Decades later, the F-35B arrives as a replacement for the legendary jump jet. Just like its predecessor, it can take off and land vertically, thanks to its massive lift fan. The most noticeable feature of the variant, the lift fan shows itself after a hatch opens just behind the cockpit during vertical takeoffs. In the rear, the Pratt & Whitney F135 points downward, giving the aircraft two points of thrust. To keep the plane stable in these configurations, two roll nozzles can guide air from the wings, giving the plane full control while sitting in mid-air.

Entering service with the Marine Corps in 2015, F-35Bs also are used by the United Kingdom and Italy, with a handful on order from Japan as well. The aircraft makes major sacrifices for its SVTOL abilities, as it has the lowest internal fuel capacity, range, and weapons payload of the trio. But just as with the Harrier, many argue its unique abilities make it more than a worthy trade-off.

C is for Carrier

For over 40 years, the F/A-18 has been an icon of the U.S. Navy and Marine Corps. The multirole fighter evolved in 1999, with the introduction of the improved F/A-18E and F “Super Hornet.” When not getting tossed into the ocean, the Super Hornet has been the tip of the spear for naval air wings over the past two decades.

For the older legacy Hornets, however, their age was starting to show, and they needed a replacement. That’s where the F-35C came into the picture, as a naval aircraft configured for catapult-assisted takeoff, but arrested recovery. But to transform a jet to fly off of America’s supercarriers, it takes far than just adding a tailhook. The landing gear is reinforced to handle both being chucked off the deck by catapult and the “controlled crash landings” on the return leg. Back on the ship, the C has a built-in ladder and folding wings to save valuable space on deck.

Unfurled, the C’s wings are actually the largest of the three, spanning 43 feet. This gives the plane the low-speed handling needed to approach and land on carriers. This added wingspan also grants the C with the most internal fuel storage — 1,500 pounds more than the F-35A. An important addition when your home base is constantly moving, and you might need a couple of tries to land.