When displaying a signal indicating doubt about another vessel’s actions, how many short blasts should be given?

Answer: D — Five

When a vessel is in doubt about another vessel's actions and needs to signal its uncertainty according to the USCG Rules of the Road, it is required to signal with a specific sequence of blasts. This signal consists of five short blasts. This standard is intended to communicate a clear message of doubt or confusion regarding the intentions of the other vessel, helping to promote safety and avoid potential collisions on the water. Using five short blasts is widely recognized and understood among mariners as the appropriate way to express this particular concern. Other signaling conventions, like one, two, or three short blasts, have different meanings related to maneuvering or intentions – for instance, one short blast indicates “I am altering my course to starboard” and two short blasts means “I am altering my course to port.” Therefore, the five short blasts specifically denote doubt, enabling an effective way to convey the need for clarity in vessel navigation situations.