[R-390] I was unaware they made this cover(pics)!

[RLucch2098 at aol.com]

Hi All;
I never seen one of these but then again I only have a few R-390A's.
Someone told me that these were used to "Hide" the receive frequency in a 
Military receiving station where they had many receivers.
Does anyone know who made these?
Where they put on or made by the Military?
This one is on a Collins R-390A
Pic:
http://www.myradioroom.com/r390adialcover1.jpg
http://www.myradioroom.com/r390adialcover2.jpg
Tnx & 73..
Rich WA2RQY