Seoul, South Korea CNN —When the presidents of the United States and South Korea this week announced a landmark deal to deter North Korean aggression, one element of the pact stood out. Here’s what you need to know about the submarine and why it’s heading to South Korea. The Nuclear Threat Initiative at the James Martin Center for Nonproliferation Studies estimates that each Trident missile can carry four nuclear warheads, meaning each US ballistic missile submarine could be carrying about 80 nuclear warheads. One arriving in South Korea on a port visit – which must be arranged 24 to 48 hours in advance – would be far more visible, giving North Korea an advantage, Schuster said. Kim’s threats have prompted some in South Korea to call for Seoul to become a nuclear-armed power itself.

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