INTERNATIONAL ONLY Your vessel is backing out of a slip in a harbor and you can see that other vessels are approaching. You should sound which of the following signals?

Correct Answer: Option D — Three short blasts when leaving the slip

Rule 34(a) requires a vessel operating astern propulsion to sound three short blasts. This signal is mandatory when a vessel is backing out of a slip or wharf, regardless of whether other vessels are sighted, to warn nearby traffic of the vessel's movement and change in propulsion status.