A U.S. Army combat brigade that has anchored the U.S. military presence in South Korea for nearly 50 years will be deactivated and replaced with a rotational unit as the service shrinks in size due to budget cuts, defense officials said on Thursday.

U.S. Defense Secretary Chuck Hagel approved deactivation of the 2nd Infantry Division's 1st Armored Brigade Combat Team effective next summer, officials said. The unit, the so-called Iron Brigade, has been permanently stationed in South Korea since 1965, staffed by individual soldiers sent to serve a year.

Army Col. Steve Warren, a Pentagon spokesman, said the move was long-planned and did not represent a reduction in U.S. commitment to South Korean security. In fact, he said, similarly sized, fully trained units would be rotated into South Korea for nine-month tours.