US tested a warhead unit for the nuclear Sentinel, deployment of which will cost $141 billion

On November 4, Lockheed Martin reported that, together with the US Air Force, it tested an experimental Mk21A warhead unit without its live nuclear payload — the W87-1 nuclear warhead with a yield of up to 475 kt. The Mk21A, which was mounted on a special test rocket vehicle, was launched from Vandenberg toward the Pacific Ocean. 

According to Lockheed Martin, the test was conducted under a military contract worth more than $1 billion. The company said the test validated the vehicle’s design and the technologies it uses for reentry into the atmosphere.

From AIN note that the Mk21A is being developed for the new intercontinental ballistic missile LGM-35A Sentinel. This unit is needed so that the W87-1 nuclear warhead it would carry can pass through the dense layers of the atmosphere and withstand the damaging effects of nuclear blasts. 

The LGM-35A Sentinel is intended to replace the Minuteman III, which entered service back in 1970. Development of the new missile began in 2020, but so far the project has encountered major problems, budget overruns, and schedule delays.

After analyzing facilities from the Minuteman III era, the US Air Force selected new hardened silos and command posts. They will be connected by protected fiber-optic lines. In March 2026 work began in Utah on a full-size prototype silo to test the design and construction methods before deployment to missile fields. The scale of the effort is evident from the Air Force plan: this approach is intended to form the basis for constructing 450 silos.

Most of the program’s cost growth has come from launch infrastructure, command posts, and the transition from Minuteman III to Sentinel. In January 2024 the Air Force informed Congress of a critical breach of planned costs. After the review required by the Nunn — McCurdy?the law that governs oversight of cost growth in U.S. defense acquisition programs, the Pentagon decided to continue the program under a revised plan.

In July 2024 the Pentagon estimated acquisition costs at $140.9 billion — 81% higher than the initial estimate of about $78 billion. In February 2026 the U.S. Government Accountability Office (GAO) assessed the program’s cost at at least $141 billion. That figure covers development, procurement, and ground infrastructure. Separately, in its fiscal year 2026 budget request the Pentagon asked for $4.2 billion for the program.

In February 2026 the GAO reported that the Sentinel’s first flight had been delayed by roughly four years from the original schedule — to March 2028. Later the Air Force changed the test plan. The first five flights are now planned to be conducted from a ground site, starting in 2027. The first silo launch, which was originally to begin the flight program, is scheduled for the third quarter of fiscal year 2030.

The Air Force expects the Sentinel to reach initial operational capability in the early 2030s. Due to delays in transitioning to the new system, it will have to continue supporting the Minuteman III for longer. The GAO estimates the old missiles could remain in service until 2050.

Read also: Poland to create a PAC-3 maintenance center for Patriot: when it could be launched and whether it will help Ukraine