Do any of you remember this?  I had a 4 hour ride to the offshore platforms I worked on in 81 or 82 and thought the new compact Wm would make the 4 hours pass a little faster.  What was neat about this sports model was it was water resistant (wouldn't have to worry about salt spray as much)and had a back up battery pack that held 2 D batterys.  I'd clip the Wm on one side of my belt and the backup battery pack on the other and jam to Uprising, Hi Infedelity, Abacab, and Back in Black (to name a few of the many cassettes I'd pack in my carry on) while leaning against the wheel house on the ride out.

here's a photo of the battery pack, my walkman was the yellow sport model made about the same time, I forget the model, I'll have to dig it out of storage.

Sony Walkman WM-2 with plastic battery case and beltclip (1980), one of the oldest Walkman models

So early in the eighties, they can may had only a WM-F5.

Was it this ?

It was the first Sports Walkman. Came in the year 1983