What might a modern convoy escort force look like, and can it be built cheaply?
Short answerA capable force would need expensive sensors, command systems, helicopters, and air defence, likely arranged as a distributed manned-and-unmanned system rather than a cheap small escort.
NotesA viewer's proposal recalls 1960s U.S. studies of merchant-hull and austere surface escorts, along with a small nuclear-powered escort submarine. Another comment points to the U.S. Navy's 1980s Maritime Strategy as an alternative that would attack the submarine threat closer to its bases instead of refighting an Atlantic convoy campaign. For a present-day convoy, sonar arrays, combat systems, data links, helicopters, anti-submarine missiles, and air-defence weapons drive ship size, electrical demand, and cost. Modern merchant ships also make enough noise to advertise the convoy to a submarine, while over-the-horizon missiles widen the defensive problem beyond close escort. A plausible force centres on a frigate or command ship linked to drones that distribute sensors and weapons around the perimeter. That network would have to keep functioning if satellites and GPS were attacked during a peer war. The result is a system of systems rather than a modern equivalent of a cheaply fitted corvette.