The world's very first UHF television station was KPTV, channel 27 in Portland, Oregon. Its FCC construction permit was issued in the first batch of same post-freeze (July 9, 1952) and it went on the air a quick two months later (September 18, 1952). Although it was a success, it nonetheless lasted less than four years, the victim of a new owner who wanted it only for its call letters and NBC network affiliation (KPTV was moved to VHF Channel 12).
This 1953 promotional film by the Zenith Radio Corporation was produced to educate Zenith dealers and the public about UHF television in general and Zenith's all-channel receivers and Zenith Terra-Tuner UHF tuning strips which was used to replace an unused VHF channel strip on a VHF-only set. Apologies in advance for the final two minutes missing.
This clip was previously on CZcams, but the channel that posted this originally has since been terminated.