Oooh, what is this nice man doing........ well, you might think he's making some sort of mine though you would be wrong. In actuality, here is a Philips technician, vibration testing a batch of experimental thyratrons and triodes for use in a European variant of the Mk 53 aerial mine's proximity fuse.
The working of these devices was rather elegant. The shell contained a miniaturised transmitter using the shell body as an antenna to emit a continuous wave of approximately 200 MHz. As the shell approached a reflective target, an interference pattern was created. As the distance to target decreased, a radiated power and corresponding oscillator supply current change would occur. The Doppler frequency shift could be tuned between the ranges of 200 - 750 Hz to trigger a detonation once a chosen amplitude was reached.