The USS Mississippi, one of the most advanced submarines in the world, docked up on the southern island of Jeju in South Korea.
With a crew of approximately 150, the 7,800-tonne Hawaii-based submarine is 114.9 metres long and 10.3 metres wide and can sail as deep as 250 metres at the maximum speed of 25 knots.
The port call comes at a time of escalating tensions between the US and North Korea, which has stepped up the pace of its nuclear weapons programme and missile provocations amid fears of World War 3.
Rear Admiral Brad Cooper, unit commander, said: “The US and ROK South Korea navies share a strong partnership that is continually strengthened by routine interactions that enhance and foster our relationship.
“This visit will allow Mississippi crew members the opportunity to enjoy the unique culture of the residents of Jeju island.”
Commander Eric J Rozek, commanding officer, said: “We are proud of our longstanding history and commitment to partnering with regional navies throughout the Indo-Asia-Pacific region.
“Through decades of exchange, training, and collaboration we have helped others build capabilities that, taken together, enhance regional security and stability.”
Today’s sub visit is likely to stir the pot even more as the war of words between Donald Trump and Kim Jong-un continues.
It comes after Mr Trump slapped the North with more sanctions in a bid to crush Kim and disband his nuclear weapons programme.
The new sanctions are aimed at hurting trade between China and North Korea a bid to pressure Pyongyang to back away from its ambition to develop a nuclear-tipped missile capable of hitting the US mainland.