The R9559 is a reflex klystron oscillator for use with an external cavity. The R5222A is of a similar design and came complete with external cavity. It is designed to work between 3.3 and 4.9 GHz and generate up to 80 mW of RF and is thus a receiver type.
The attached data is taken from:- British Special Quality Valves and Electron Tube Devices Data Annual 1964-65 pp858. Found on Google books.
The cathode is on the left with connections to the external cavity seen as the brass ring and flange, the latter is 36 mm in diameter.
The cavity connection shown on the left appears to have a wire mesh over the opening.
The thin glass tube envelope is 18 mm in diameter, and excluding the base pins is 85 mm tall.