Which vessels sound the same signal while underway and at anchor?

The correct answer focuses on the fact that vessels constrained by their draft (RAM) and fishing vessels, when both are operating underway and at anchor, are required to sound the same signal to communicate their status effectively. According to the International Regulations for Preventing Collisions at Sea (COLREGs), when a vessel is constrained by her draft or engaged in fishing and is at anchor, it should sound one short blast on the horn or whistle.

The similarity in signaling ensures that other vessels nearby understand the particular status of these vessels, which can be critical in avoiding collisions and ensuring safe navigation. Additionally, both RAM and fishing vessels face unique navigational challenges that necessitate clear communication with other maritime traffic.

Other types of vessels may sound different signals depending on their status (either underway or at anchor) or the nature of their operations. For example, a vessel not under command or a sailing vessel may have different signaling requirements that do not overlap with those of RAM vessels or fishing vessels. Similarly, the notion that all vessels or only merchant ships would follow a singular signaling pattern does not account for the specific requirements laid out for distinct vessel categories.