Which of the following would be classified as a "special circumstance" under maritime rules?

A "special circumstance" under maritime rules generally refers to situations that require additional considerations for safe navigation and collision avoidance beyond the usual conventions. The scenario where more than two vessels are meeting qualifies as a special circumstance because it complicates the navigation and the interactions between the vessels involved.

When multiple vessels are involved in close proximity, the likelihood of confusion increases regarding the actions each vessel should take, which amplifies the potential for collisions. The presence of additional vessels means that each must be aware of not only its maneuvers but also how the other vessels are likely to respond, which can alter their course, speed, and overall navigation strategy.

This complexity in navigation requires extra caution and consideration, hence it is designated as a "special circumstance" under maritime rules. In contrast, a vessel at anchor, speed in fog, and two vessels crossing are all situations that are covered under standard navigation rules and have established protocols for handling, rather than qualifying as special circumstances.