Which vessel would NOT sound a fog signal of one prolonged blast and two short blasts?

• A. A vessel being towed
• B. A power-driven vessel underway in fog
• C. A sailing vessel under sail
• D. A vessel at anchor in fog

Answer: (A)

The main concept is that one prolonged blast followed by two short blasts is the standard fog signal for a power-driven vessel underway in restricted visibility. A vessel being towed is not under its own power, and its tow status calls for a different signaling pattern to warn others of the tow arrangement and the lack of independent propulsion. So this vessel would not emit the one-long-two-short sequence. The other scenarios described involve vessels that, under the rules, would use the standard power-driven underway signal when conditions require it, or would follow their own distinct signaling patterns if they’re in a different situation (such as being anchored).