The USS Michigan, which is a guided missile submarine, arrived in the port city of Busan, South Korea, on Tuesday. A US military official described the move as a show of force.
Washington has already sent the USS Carl Vinson aircraft carrier strike group to the western Pacific Ocean.
The Ohio class submarine will later join the aircraft carrier for exercises in the Sea of Japan.
The movement came after North Korea threatened to sink USS Carl Vinson.
“Our revolutionary forces are combat-ready to sink a US nuclear-powered aircraft carrier with a single strike,” the ruling Workers’ Party’s newspaper said in a commentary on Sunday.
The article said Pyongyang had weaponry that “can reach continental US and Asia Pacific region.”
A statement from US Naval Forces Korea described the submarine’s visit as “routine deployment.”
“US Navy ships and submarines routinely make port calls in a variety of locations,” Lieutenant commander Matt Knight with US Pacific Fleet told Fox News.
“As a matter of routine, we do not discuss future operations or the details regarding the operations of our submarines. USS Michigan is currently on a routine deployment to the Indo-Asia-Pacific.”