Which situation does not require a sound signal under international rules?

Answer: C — Meeting or crossing international

In the context of international maritime regulations, the scenario that does not require a sound signal is when meeting or crossing international waters. According to COLREGs, sound signals are primarily utilized in situations to communicate intentions between vessels in close quarters, particularly when the likelihood of collision exists. When vessels are in international waters, they are typically beyond the narrow channel or areas of congested traffic where the exact navigation of each vessel can be more challenging. Therefore, the rules governing sound signals focus on more congested or potentially hazardous situations, such as those found in narrow channels, during overtaking maneuvers, or in conditions of restricted visibility where increased caution and communication become essential. In summary, while sound signals are critical in situations where the positioning of vessels may lead to confusion or risk of collision, operations in open international waters are generally less prone to such hazards and do not mandate the use of sound signals for navigation purposes.