Glad when I can provide a smile, Suki. And I'm always happy when I can say "you're both right". As a big a blowhard as I am, I actually don't like to argue. As someone with a degree in broadcasting and an amateur historian, here's a little 411. As you likely know, many TV classics started out as radio hits. Gunsmoke is another example, and I Love Lucy came about because Lucy's first big success was a radio sitcom called My Favorite Husband. In fact, Gail Gordon - Mr. Mooney from the Lucy Show - was one of the supporting actors in that show.
Jack Webb's Joe Friday had more than one partner. The original radio partner was Ben Romero - played by Barton Yarbrough. The series, though still on radio, started on TV for 8 years in '51. Yarbrough died right at the beginning so they gave Friday a new partner. First, Ed Jacobs - Barney Phillips - then Frank Smith, played by Ben Alexander. Webb and Alexander clicked and Smith became the most well known partner.
And, of course, your already know you're right about Harry Morgan playing Bill Gannon in the color revival of the series. For my money, Morgan was the best sidekick. He was the best in playing low key yet quirky at the same time.
If you haven't already seen it, here's the Wiki:
http://en.wikipedia.org/wiki/Dragnet_(series)
Yeah, a lot of neat stuff on Hulu. You like sexy and suave guys? Check out Robert Wagner in "It Takes a Thief". That'll make your hubby jealous! LOL