While being assisted by an icebreaker on Lake Superior, you receive a single letter code instructing you to slow your vessel. Which signal could you use to signify that you are complying with the request?

Correct Answer: Option D — Four blasts of the whistle, namely 1 short 2 long and 1 short

Standard ice-assist whistle signals prescribed by maritime authorities require the assisted vessel to acknowledge speed reduction instructions using the Morse letter 'R' sound signal: one short, two long, and one short blast (Morse code 'R').