On Saturday morning a squadron of F-35Bs taxied onto the flight line at Marine Corps Air Station Iwakuni, on the Seto Inland Sea, and took over a job the US Marine Corps has been rotating through Japan since 1980.

The unit is Marine Fighter Attack Squadron 533, the Hawks, from MCAS Beaufort in South Carolina. It is their first Unit Deployment Program rotation on the F-35B, and it closes a chapter that ran for decades on the F/A-18D Hornet.

There is a neat piece of symmetry in it. When the Unit Deployment Program began in 1980, the first unit to deploy under it was VMFA-533’s own predecessor squadron.

What the Unit Deployment Program actually is

It is one of the quieter but more consequential ideas in American military aviation, and it solves a specific problem: how do you keep combat squadrons permanently available in the Indo-Pacific without permanently moving thousands of Marines and their families to Japan?

The answer is rotation. Units based in the continental United States cycle through Iwakuni for a defined period, fly and train in the region, then hand the slot to the next squadron and go home. The aircraft change, the squadron patch changes, the capability at Iwakuni does not.

The Marine Corps has run this since 1980. VMFA-533 has done it before, most recently in 2018, but that rotation was flown with Hornets.

From Hornet to Lightning

The Hawks received their first F-35B at Beaufort on 11 October 2024, after decades operating the two-seat F/A-18D. That transition is close to universal now across Marine fighter squadrons, and it changes what a rotation like this can do.

The F/A-18D was a capable strike fighter that needed a runway. The F-35B does not, at least not a long one. Short takeoff and vertical landing means the squadron can operate from an amphibious assault ship, a damaged airfield, or a stretch of road with matting laid on it — which is precisely the point of the Marine Corps’ current Pacific concept of dispersing small detachments across many locations rather than concentrating them at a handful of large bases.

The phrase “naval and expeditionary sites” is doing a lot of work in that sentence. It is the difference between a squadron that needs Iwakuni and a squadron that can leave it.

Iwakuni is getting crowded

MCAS Iwakuni is one of the more interesting airfields in the world for anyone who likes military aircraft. It already hosts other Marine F-35B squadrons alongside F/A-18D Hornets and KC-130J tankers, and it supports elements of the US Navy’s Carrier Air Wing 5, the air wing that operates from the forward-deployed carrier in Japan.

Add a rotational F-35B squadron on top of that and you have a single base holding fifth-generation fighters, legacy Hornets, tankers and carrier air wing assets, roughly 900 kilometres from the Korean Peninsula and well within reach of the East China Sea.

US Marine Corps F-35B operations in Japan.

What was not said

The Marine Corps did not disclose how many aircraft or personnel came with VMFA-533, or how long the rotation will run. That is normal for a UDP deployment and mildly frustrating for anyone trying to count airframes.

What it does tell you is straightforward enough. The rotational fighter slot in Japan is now a fifth-generation slot, flown by an aircraft that does not strictly need the runway it landed on.

Sources: US Marine Corps release and imagery; The Defence Blog.