Ballistic Missile Submarine's (SSBNs) Mission Statement

The U.S. Navy's ballistic missile submarines, commonly known as
"boomers," serve as hidden, undetectable launch platforms for
Submarine Launched Ballistic Missiles (SLBMs). The submarines
are designed specifically for stealth, and the precise delivery of
nuclear warheads.

As the third tier of the U.S. nuclear triad, their primary mission is
nuclear deterrence.