I agree that UHF equipment was available from the mid 50s but by "viable" I mean I do not believe performance was comparable to VHF in reliablity for critical Public Safety use.
As a user of the T-44, I'd have to disagree. It was as reliable as any of the VHF boat anchors of the time.
I have been involved with 2-way service since 1962 and I did not consider these early UHF radios as "very nice". I do consider VHF and Low Band versions of equipment from that era true classics that performed very well for a long time but not so for their UHF counterparts.
I'd stack a T-44 against a GE VHF-lo pre-Prog any time.
Sensitivity of early UHF radios was terrible by todays standards, maybe 1uV with new tubes and recently aligned.
About the same as the VHF receivers of the time.
The life and efficiency of the final tubes was poor and the radios were just not very reliable.
I replaced VERY few lighthouse tubes. Fewer than the 829Bs I replaced.
Yes, there were a lot sold, manly for urban taxi use. The whole state of the art for UHF then was limited by poor equipment stability, lossy feedlines, poor antennas, low base station power etc.. that made it not generally competetive when VHF or Low Band was an option.
Lossy feedlines, connectors that were designed to work up to about 30MHz, low gain antennas and low power (base and mobile) because generating high power at 450 was more difficult then than generating high power at 1.9GHz is today.
But the equipment was viable. I still have a few working T-44s - with the original 2C39s. (And I may still have a working U44BBT modified into a repeater buried in the old radio stack.)
I found it was the mid 60s with the development of repeater systems along with radios like the original GE MASTR series that made UHF competetive with other bands for widespread use. I remember the first UHF MASTR repeater system we installed for a business user and we were amazed by the performance compared to prior experience with UHF.
UHF simplex is no worse than VHF simplex, allowing for the shorter range due to the higher frequency. Which has nothing to do with the viability of the radios.
NYPD stayed with VHF until the shared UHF TV spectrum became available. I beleive the huge increase in available channels was the main reason NYPD moved to UHF.
That, and a few other things - like much of the city was already on UHF (Sanitation, Traffic, etc.)