Thanks for help with identification Hanno, all I need now is the small hatch Sherman to go with it! After I posted the second bunch of photos I got to thinking about a similar item I had bought 25 years ago. They were similar windshield type fixtures. I thought I had sold them all but I went out this morning to my storage yard and went digging. I found two left in a racoon infested bus ( gloves, mask and spray disinfectant required) and offer up a couple of photos. These must be 1950s NATO but I have no idea what application. They look very similar!
defrost3.jpg defrost1.jpg defrost2.jpg defrost4.jpg