I think Police Squad was a film version of Naked Gun.
Nope. Police Squad! came first, but was a huge flop on TV and only lasted about 6 episodes. The Naked Gun was a theatrical release "From the files of Police Squad" and came later. It was successful enough to spawn a couple of sequels.
The first episode of Police Squad! is based on a specific episode of M-Squad. For some reason, the "Airplane" style humor doesn't work well on TV. Take a look at Angie Tribeca sometime.