What kind of signal would be used to announce an enemy attack?

The use of a 3-to-5-minute wavering sound on sirens to announce an enemy attack is effective because it is designed to quickly capture attention and convey urgency. Wavering sounds are easily distinguishable from other sounds and can signal an immediate threat, prompting people to take action and seek shelter or listen for further instructions. This type of alert is often employed in emergency situations because it stands out and resonates in various environments, ensuring that it reaches as many individuals as possible, even in high-stress situations.

Other options may not provide the same level of urgency or clarity. For instance, a sustained single tone might fail to convey an immediate threat effectively, while a series of short blasts on a horn could be confused with other signals. A steady sound might not convey the critical urgency that a wavering tone does, which makes the wavering siren sound especially effective for alerts concerning immediate danger.