What is the action required by the give-way vessel according to Rule 15?

Answer: A — Take early and substantial action to keep clear

The requirement for the give-way vessel under Rule 15 is to take early and substantial action to keep clear of the stand-on vessel. This is crucial in preventing collisions and ensuring safe navigation on the water. The essence of this rule is that when two vessels are approaching each other with a risk of collision, the give-way vessel must take affirmative steps to yield its right of way. This includes not only recognizing the situation but also implementing a response that is timely and clearly communicates an intention to avoid a collision. The actions taken should allow the stand-on vessel to continue on its course without the need for it to alter its path or speed abruptly, maintaining overall safety on the water. Other options suggest maintaining course and speed, making abrupt changes, or signaling intentions, but these do not fulfill the primary responsibility of the give-way vessel to yield and ensure safe passage by altering its course or speed as necessary. Thus, taking early and substantial action to keep clear encapsulates the essence of Rule 15.