SSBN (Ballistic Missile Submarines)
- Nuclear-propelled submarines designed for carrying multiple sets of submarine-launched ballistic missiles (SLBMs), often tipped with single or multiple nuclear warheads.
- The primary mission is to provide a devastating retaliation or assured second-strike capability, fulfilling the third leg of the nuclear triad.
SSN (Nuclear Attack Submarines)
- SSNs have infinite capacity to stay dived. As they are not propelled by batteries, they need not emerge for charging by a diesel engine.
- Propelled by a nuclear-powered engine, these submarines only need to come to the surface for replenishing supplies for the crew.
SSK (Original Diesel-Electric Submarine)
- Originally designed and constructed as diesel-electric submarines. They require air and fuel to operate.
- They need to resurface more frequently.