SHORAN was sent into combat due to the presence of the MiG-15 over Korea, which drove the B-29's from daylight combat in June 1951. Night operations were not very productive and the US Air Force became interested in any way to improve their results. The system was in place and the crews trained by November 1952, and SHORAN remained in use from then until the end of the war. It was particularly effective during early 1953 when the North Korean Air Force began to re-equip in case a new offense opened. B-29's began the campaign, but only a dozen aircraft were available, so they were soon supplanted by B-26s to maintain constant bombing of the airfields. The possible offensive never occurred; the armistice was signed in July. It was not used after that point, due to Strategic Air Command's increasing focus on long-range bombing with nuclear weapons.