The distance a vessel moves at right angles to the original course, when a turn of 180° has been completed, is called the __________.

Correct Answer: Option B — tactical diameter

Tactical diameter is the distance a vessel travels at right angles to its original course after completing a 180-degree turn. This measurement is essential for determining the space required for emergency maneuvers and is a standard component of a vessel's maneuvering data required by IMO and USCG standards.