This is a type 417 reflex klystron with a 'WL' prefix. The 'WL' prefix indicates the manufacturer. Small klystrons of this class were widely used as local oscillators in radar receivers. The 417A was used in the Radio Set AN/CPN-3 but we have no details on the 417, it may be that the A has rubbed off.
The 417A was designed to operate at 2.65 to 3.33 GHz and generate 250 mW of RF. The cavity is integral to the design and the tuning is mechanical. The RF connectors can be seen to be co-axial.
They were normally tunable over a modest range and were adjusted to be exactly in tune with the (much more powerful) pulse transmitting valve (usually a cavity magnetron). The magnetron generated an RF output only briefly, when pulsed, but the klystron provided a continuous low-level RF signal which could be used to 'beat' (mix) with the faint echo signals in order to reveal small frequency differences of Doppler shifted echoes from moving aircraft.
The lever on the right is the tuning mechanism. Pushing it closer to the valve body will increase the distance between the top and bottom of the resonator - lowering the frequency. The three screws set the maximum frequency.
A threaded rod pushing on the tuning leaver would make contact at the plain section at the top.
The reflector connection.
The lower connections give little detail of the inner structure.
The wide metal tube envelope is 32 mm in diameter and, excluding the IO base pins, is 113 mm tall.