A partly submerged object that is 25 meters or more in breadth must display which type of lights at its greatest breadth on both sides?

A partly submerged object that is 25 meters or more in breadth must display all-around white lights at its greatest breadth on both sides to ensure visibility and safety for navigation. The use of all-around white lights indicates that the object is potentially a hazard for vessels navigating nearby. This is in accordance with the International Regulations for Preventing Collisions at Sea (COLREGs), which require certain signaling for large floating or submerged objects to alert other mariners of their presence, especially during nighttime or low-visibility conditions.

The specification of displaying the lights at the greatest breadth emphasizes that the lights need to be positioned where they can provide the best visibility across the widest part of the object. This setup helps other vessels recognize the dimensions and the potential danger posed by the obstruction in the water.

While red and green lights are generally used to indicate the port (left) and starboard (right) sides of vessels, they are not appropriate for a partly submerged object of this nature. Sidelights also would not apply, as they are designated for vessels underway rather than for objects that are stationary or at anchor. Thus, the requirement for all-around white lights directly addresses the need for clarity and safety in navigation around such obstacles.