BOTH INTERNATIONAL & INLAND While underway and in sight of another vessel, less than one half mile away, you put your engines on astern propulsion. Which statement concerning whistle signals is TRUE?

Correct Answer: Option B — You must sound three short blasts on the whistle.

Rule 34(a) requires that when vessels are in sight of one another, a power-driven vessel maneuvering as authorized or required by these Rules shall indicate that maneuver by the prescribed whistle signals. Three short blasts specifically indicate that the vessel is operating astern propulsion, regardless of the vessel's heading.