Final answer:
The first fleet ballistic missile submarine was launched in 1955.
Step-by-step explanation:
The first fleet ballistic missile submarine was launched in 1955. During the 1950s, both the United States and the USSR developed intercontinental ballistic missiles (ICBMs) and submarines that could launch them. The first submarine of this kind was the USS George Washington, a Polaris-class submarine launched in 1959.