Fisher's Blend Station bought NBC Blue Network affiliate KJR from NBC in 1941. However, the August 1941 adoption of the Federal Communications Commission's "duopoly" rule restricted licensees from operating more than one radio station in a given market, and an attempt by the Fisher family to be granted an exemption was unsuccessful. The Fishers decided to keep the superior frequency of 1000 kHz, but also keep the KOMO call letters that they had held since the 1920s. Thus, on May 6, 1944 KOMO and KJR swapped call letters, with the KOMO call sign moving from 950 kHz to the more desirable 1000 kHz. The next year KJR was sold to Birt F. Fisher, who was unrelated to the KOMO owners.