It is simply indicating that it is in gear.
What does the wavering tone warning signal alert a base for
What is the wavering tone warning signal alerts the base
attack
attack
attack
A three to five minute wavering tone on a siren or similar warning device indicates that an attack or hostile act is imminent or in progress.
Tone - magazine - was created in 1999.
air attack
Air Attacks
air attack
air attack
air attacks