Mk21A: flight test over the Pacific for the reentry vehicle that will carry the new ICBM’s nuclear warhead

The Mk21A, the new reentry vehicle that will carry the nuclear warhead of the future American intercontinental ballistic missile, has completed a test flight over the Pacific Ocean. Lockheed Martin announced on Wednesday, November 4 that, together with the US Air Force, it launched an unarmed development Mk21A reentry vehicle from Vandenberg Space Force Base in California. According to the company, the flight showed that the vehicle’s architecture has matured and validated the next-generation reentry technologies it incorporates.

In its announcement the company describes the Mk21A as a complete next-generation reentry vehicle that will be the payload atop the future intercontinental ballistic missile (ICBM) system. The programme, which modernises the older Mk21, runs on a prime contract worth more than $1 billion and concerns the land-based leg of the US strategic nuclear triad.

From digital design to flight

Lockheed Martin says that to speed up development it combined data from earlier tests with digital engineering tools and high-fidelity simulations. The data from the new flight will lead to design improvements and shape the next tests, as the programme moves towards a system-level Critical Design Review (CDR).

“Testing is a rigorous requirement in modern defence programmes, but above all it is the driving force for maturity and reliability,” said Jason Watson, Lockheed Martin’s vice president for strategic reentry programmes. He said the company is turning experience from earlier flights into programme progress, so that the vehicle gives the Air Force uncompromising performance.

The W87-1 warhead and the Sentinel

The Mk21A is intended for the new LGM-35A Sentinel intercontinental missile, being developed by Northrop Grumman to replace the Minuteman III, and is designed to carry the new W87-1 nuclear warhead. The Sentinel programme is even considering buying land for up to 120 new silos, while L3Harris is sextupling production of large rocket motors for it.

The vehicle’s immediately preceding test, announced by the Air Force, took place on the morning of October 9, also from Vandenberg, with a Northrop Grumman Minotaur I rocket. That was a flight environment test, overseen by the Space Force’s Rocket Systems Launch Program. Brig. Gen. William Rogers, responsible for ICBM programmes at the Air Force Nuclear Weapons Center (AFNWC), called the Mk21A “vital to modernising our ICBMs” against a fast-changing picture of adversary threats. Before that, on June 17, 2024, the heat shield was successfully tested, as a Pentagon report notes.

The AFNWC awarded Lockheed Martin a $996 million contract in October 2023, supplemented by a $453 million modification in November 2025 under a new programme baseline which, as a Pentagon report notes, decouples its schedule from external programmes. The Critical Design Review for the whole Mk21A is scheduled for March 2027, and for its development the Air Force requested nearly $540 million in the fiscal 2027 budget request, $184 million more than in 2026.