What is the designation for a nuclear submarine?

The designation for a nuclear submarine is represented by the code "SSN," where 'SS' stands for "Submersible Ship" and 'N' signifies that it is nuclear-powered. This classification encompasses all types of nuclear attack submarines, which are designed to carry out various missions including anti-surface and anti-submarine warfare, intelligence gathering, and land attack.

When looking at other designations, "SSBN" refers specifically to ballistic missile submarines, indicating a different class of nuclear submarines with a focus on strategic nuclear deterrence. The designation "SS" alone is a general term that might refer to submersibles but does not specify the nuclear capability. "SSN-688," on the other hand, identifies a particular class of attack submarines known as the Los Angeles-class, and while it is part of the SSN group, it denotes a specific design rather than the general classification.

Thus, "SSN" accurately captures the broader category of nuclear submarines, making it the correct answer.