Since June, Coast Guard vessels patrolling the US’s southern approaches have stopped seven low-profile smuggling vessels — stealthy ships that ride low in the water to spirit illicit cargos from South America to Mexico and the US.

Akin to self-propelled semi-submersibles used by smugglers for the same purpose, low-profile vessels are boats designed to run near or at surface level to present the smallest possible radar signature.

Low-profile vessels usually have a sharp bow to cut through the water and an elongated body to transport cargo — typically high-value drugs like cocaine. Some only have masts or conning towers that stick out above water, and they are often outfitted with multiple outboard engines and painted to blend in with the water.