The United States has reached a milestone in building the Navy's first next-generation submarine equipped with nuclear missiles as it races to modernize its air-, land- and sea-based strategic forces against Russia and China.

Newsweek has reached out to the Russian Foreign Ministry for comment via email. The Chinese Foreign Ministry did not immediately respond to a request for comment.

Why It Matters

The U.S. has the world's second-largest nuclear arsenal by number of warheads, with 3,700 available for use by its nuclear triad —intercontinental ballistic missiles , ballistic missile submarines and nuclear-capable aircraft—ensuring the nation can respond to a nuclear attack under any circumstances.

As Russia and China, the world's largest and third-largest nuclear powers, respe

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