Longines Watch Co. Issued in 1976 to commemorate bicentennial of American Revolution.
It was issued in only 200 pieces and this one is #16 of 200.

The case measures 46.27 mm across and is quite heavy weighing 61.2 grams.​

 

Wonder why they didn't use a larger caliber seeing as they had the room?

 

Who knows. Here is another one. This one in platinum with silver dial.

 

I think this was their most modern manual wind movement at the time, so maybe the default choice? It certainly does disappear in that monster case! That's gotta be dense sucker.

 

Both cool pieces. I have seen the bicentennial before but that octagon is pretty cool.