The correct answer is D) Single luff tackle. The single luff tackle, also known as a single whip or a single part tackle, is a type of tackle consisting of a single rope or cable that runs through a single block or pulley. This configuration allows for a mechanical advantage when lifting or pulling loads, making it a common choice for various tasks on Coast Guard vessels. The other options are incorrect: A) 1-2 purchase refers to a more complex tackle system with multiple parts, B) Gun tackle has a different configuration with two blocks, and C) Double whip is a separate type of tackle with two separate ropes or cables.