A whistle is recommended as a signal device for a small unit leader because it is lightweight, compact, and can produce a loud sound that carries over distances, making it effective in communicating commands or alerts without the need for voice communication. In situations where verbal instructions might not be heard due to environmental noise, a whistle can quickly grab attention and convey important signals to the troops.
Additionally, using a whistle liberates a leader's hands for other tasks and does not require batteries, as is the case with devices like radios or flashlights. This simplicity and reliability make it an ideal choice for signaling in various conditions. It can also serve multiple purposes, such as signaling for assembly or warning of danger, ensuring versatility in operational situations.