A naval drifter is a boat built along the lines of a commercial fishing drifter but fitted out for naval purposes. The use of naval drifters is paralleled by the use of naval trawlers.

Fishing trawlers were designed to tow heavy trawls, so they were easily adapted to tow minesweepers, with the crew and layout already suited to the task. Drifters were robust boats built, like trawlers, to work in most weather conditions, but designed to deploy and retrieve drift nets. They were generally smaller and slower than trawlers. If requisitioned by navies, they were typically armed with an anti-submarine gun and depth charges and used to maintain and patrol anti-submarine nets.

Like fishing trawlers, the Royal Navy requisitioned many fishing drifters for conversion to naval use during World War I.

In addition, 362 naval drifters were ordered to Admiralty specifications (and thus are often referred to as "Admiralty drifters"). Shipyards used to building fishing trawlers or drifters could easily switch to constructing naval versions. As a bonus these drifters could be sold to commercial fishing interests when the war ended.