Metallic vertical blimp-shaped object

Sometime between 1971 and 1977 (I'm sorry that I can't be more specific, but we took so many trips to Florida back then and I didn't record the info), 
My then husband and I were travelling south through the Florida Keys.  As we were about to exit one of the bridges onto a Key, going South, on my right (the Gulf of Mexico side) I saw the bottom of a huge metallic "Ship" - that's the only way I can describe it, hovering near and just above a waterfront home rooftop, straddling the rooftop and the water.  It just hung there, just at a little above rooftop level.  
I could only see the bottom of it, as I remember the top of it was cloud or mist covered (although it was sitting not far off the ground).  There were lots of people already pulled over to the side of the road and out of their cars, gesturing and pointing towards it.  
I absolutely begged my then husband to please stop, stop, I wanted to look at it, but he wouldn't, just kept looking straight ahead with the pedal to the metal.  (I think he was scared to death).  I craned my neck as we drove by to see as best I could, and then it suddenly vanished.  
This happened so long ago, but I distinctly remember that whatever it was created absolutely no sound.  As to its shape, it looked to me like the rear end of a dirigible, only standing straight up, vertically.  Like the bottom of a missile.  Metallic gray.
Witness indicates that the date of the incident is approximate.  We have assigned an arbitrary date in June 1975.  PD