What does it mean for a vessel to be "not under command"?

A vessel classified as "not under command" is one that is unable to maneuver due to exceptional circumstances that prevent it from safely taking action to avoid a collision. This may include situations such as engine failure, steering gear malfunction, or encountering severe conditions that impede its ability to navigate effectively.

In this classification, the vessel is considered to be in a state where it cannot comply with the maritime rules and obligations necessary for safe navigation. Significantly, being "not under command" requires the vessel to signal its condition using appropriate sound signals and visual signals, such as displaying two circular shapes vertically. This alerts other vessels to the fact that it is unable to take actions that would typically be expected under COLREGs rules.

The other options do not accurately define the term "not under command." For instance, deliberately not moving does not imply an inability to maneuver; it implies a choice. Being anchored in place refers to a vessel that is stationary under its own power, while being towed indicates that a vessel is still operational but reliant on another vessel for movement. Each of these situations does not fit the definition of being unable to maneuver due to exceptional circumstances.