yup it's watercooled. But cant say i reconize it. Haas lots of glass -
somewhat remininicent or the kind of stuf used in the 60's. Maybe even
before. Later microwave or vacumm tube devices were usually ceramic.
The glass ed might be for optical use (like a high powered xeon flash
device that ws used in photogramic air missions). But it could also
simply be a medium high power microwave output tube.
Sorry, that's the best i can do for you.

rob