The US "Sentinel" nuclear bomb takes an important step and the new nuclear warhead vehicle is successfully tested

The picture shows a schematic diagram of the Mk21A re-entry flight vehicle. (Picture taken from Loma)

[Reporter Wu Zheyu/Taipei Report] The United States continues to promote the modernization of land-based nuclear weapons. The U.S. Air Force Nuclear Weapons Center successfully conducted a flight test of the new Mk21A reentry vehicle at Vandenberg Space Force Base in California on the 9th using the "Minotaur I" launch vehicle. In the future, this vehicle will be equipped with a W87-1 nuclear warhead and integrated into the new generation LGM-35 "Sentinel" intercontinental ballistic missile, gradually replacing the "Minuteman III" that has been in service for decades and becoming an important part of the United States' land-based nuclear deterrent capability.

The military news website "Air & Space Forces Magazine" reported that this test launch did not carry a nuclear warhead. It was also the first time the US military announced the Mk21A re-entry vehicle flight test since June 2024. After formal deployment in the future, the Mk21A will enter space through the three-stage rocket propulsion system of the "Sentinel" missile, then re-enter the atmosphere and deliver the nuclear warhead to the designated target.

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The Mk21A was developed by Lockheed Martin and is based on the Mk21 re-entry vehicle currently used by the "Zoumoire III". The "Minotaur I" rocket launched this time aboard the Mk21A was provided by Northrop Grumman. It used rocket engine technology derived from the "Peacekeeper" and "Zouoy" missiles, and was supervised by the U.S. Space Force for testing.

In terms of research and development funding, the U.S. Air Force Nuclear Weapons Center awarded Lockheed Martin a US$996 million (approximately NT$32.05 billion) contract in October 2023, and added an additional US$453 million (approximately NT$14.58 billion) contract modification in November 2025 to promote the subsequent development and testing of the Mk21A.

However, the Sentinel intercontinental ballistic missile program has been affected by rising costs and schedule delays in recent years. It has previously triggered a mandatory review by the Pentagon. It is still undergoing program reorganization and has not yet passed the "Milestone B" review required to enter the engineering and manufacturing development stage.

According to the procurement report released by the U.S. Department of Defense in September, the Mk21A has also simultaneously adjusted its research and development benchmarks, hoping to reduce dependence on other project schedules and adopt a new flight test strategy. The report pointed out that the performance of the re-entry vehicle heat shield was successfully verified in June 2024, and Lockheed Martin continued to integrate the weapon and fuze subsystems in February this year.

The U.S. Air Force plans to complete the key design review of the entire Sentinel system by March 2027 and apply for a Mk21A R&D budget of nearly US$540 million (approximately NT$1.73 billion) in fiscal year 2027, an increase of US$184 million (approximately NT$5.92 billion) from the previous year to support subsequent system integration and flight testing.