The FCC's duopoly rule, passed in 1945, prohibited the ownership of two stations by a single entity in the same community. That forced the breakup of all the NBC-organized station pairs around the country who carried both the NBC networks. (The FCC would later force NBC to sell its Blue Network two years later, which became the ABC Radio Network.)
This photo shows the "Ribbon Cutting" ceremony that took place in 1945, separating the ownerships of KOMO and KJR. O. W. Fisher (left) retained the ownership of KOMO for the Fisher's Blend Station, while Birt Fisher (right - no relation), the KOMO-KJR manager, became the new owner of KJR. The secretaries of the two executives, Marion Bush and Jean Wylie, wielded the scissors.
As a part of the separation of ownership, KOMO and KJR swapped call signs on their respective frequencies. This allowed Fisher's Blend Station to retain the KOMO call sign, the Red Network affiliation, and also gave it the ability to increase power to 50 kW. The 1944 letter below, from the FCC files at the National Archives in Washington, D.C., officially requests the call sign swap.