The ML-7815 is a high μ rugged UHF planar triode for use up to 3 GHz. The anode connection is designed for conduction cooling, and the intended application is in airborne equipment.
The valve is seen standing on the anode connector with the co-axial heater connection at the top. The envelope is ceramic and the electrode connections are silver plated. In use the valve would sit in a resonant co-axial cavity.
This shows the valve connections. Centre is heater with the other heater surrounding it. Next is the grid ring and finally the anode ring.
The planar envelope is 30 mm in diameter, and including connections is 67 mm tall.
Reference: Datasheet. Type ML7815 was first introduced in 1966.