"The Los Angeles-class fast-attack submarine USS Springfield (SSN 761) pulled into port in Busan, Feb. 23," the fleet said on social media.
Los Angeles-class submarines make routine port calls in South Korea as part of the US navy's forward-deployed submarine force in the Indo-Pacific. The length of the submarine's stay was not revealed.
USS Springfield is billed as one of the most capable ships in the entire US navy. Its homeport is in Guam, in the western Pacific.
The US Indo-Pacific Command said this week that it would maintain close cooperation with South Korean forces in light of North Korea’s "recent aggressive nuclear policy and advancements in nuclear capabilities."
North Korea has repeatedly warned the allies against building up military presence near the Korean peninsula and has criticized US-South Korean joint drills as a preparation for invasion. It has launched several ballistic missiles off the eastern coast since the start of the year.