Similar in size to corvettes, all five Class 420/Thetis-class vessels were built by Rolandwerft, Bremen.

Although they were designed, built, and designated as Subchasers by the German Navy, subchasers became obsolete after the Second World War due to being unable to keep pace with advancements in submarine technology.

Because the ships were designed to chase more modern submarines, they are more commonly referred to as gunboats.

Later the A/S mortars were replaced by a second 40 mm gun and the single torpedo tubes by triple mountings.

Upgrades started in 2000 may have included enclosed 40 mm gun mountings[citation needed] and Rheinmetall 20 mm guns to replace the MGs.