Explanation: An oscilloscope is essential for RADAR servicing because radar systems operate by transmitting and receiving precisely shaped RF pulses. An oscilloscope allows technicians to visually inspect these waveforms in the time domain, displaying critical parameters such as pulse width, pulse repetition frequency (PRF), pulse shape, amplitude, and timing relationships between transmitted and received signals. This visual representation is invaluable for diagnosing issues with the modulator, transmitter, receiver, and timing circuits. A frequency counter would only show the carrier frequency, not the pulse characteristics. An R.F. Wattmeter measures power but provides no information about the pulse shape or timing. An audio generator is designed for low-frequency audio signals and is entirely unsuitable for RF radar frequencies.