INTERNATIONAL ONLY You are on a power-driven vessel, maneuvering as authorized, and are in sight of another vessel. You put your engines full speed astern, which statement concerning whistle signals is TRUE?

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

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