Why use a spy ship when every warship can listen?

Why build dedicated intelligence ships when ordinary warships already collect electronic information?

A specialist vessel can listen covertly near ports and exploit a civilian appearance that makes interference diplomatically difficult.

Ordinary warships can collect signals, so a dedicated vessel is unnecessary for every task. A merchant or fishing identity can enter places where a recognizable combatant would attract attention. The same civilian appearance lets a collector operate without openly announcing a naval mission. Boarding a Soviet trawler created a diplomatic problem because the state owned the vessel and could treat it as national property. The legal and political shield was therefore part of the intelligence system alongside the listening equipment.