Final answer:
An acoustic mine is fired by the initiation of an enclosed microphone which picks up sound waves generated by a nearby ship's rotating screws or other operating machinery. It detects the characteristic sound frequencies of a ship's machinery and triggers an explosion.
Step-by-step explanation:
The type of mine that is fired by the initiation of an enclosed microphone which picks up sound waves generated by a nearby ship's rotating screws or other operating machinery is acoustic mine. An acoustic mine detects the sound vibrations in the water and produces a detonation when it detects the characteristic sound frequencies of a ship's machinery. The microphone inside the mine acts as a sensor, picking up the sound waves and triggering the explosion. This type of mine is commonly used in naval warfare as a defensive measure.