The Icelandic fishing fleet as the Royal Navy's surprising opponent

Which unexpected national fleet can claim to have defeated the Royal Navy?

Iceland's fishing fleet is the joking choice, because strong French and Spanish fleets are much less surprising opponents.

Iceland's fishing fleet is offered jokingly as an unusually surprising opponent for the Royal Navy. Familiar defeats by French or Spanish fleets are less unexpected because those opponents often possessed substantial naval strength at the time. The comparison concerns how surprising an opponent seems, rather than a claim that fishing vessels won a conventional fleet battle. It distinguishes an unexpected maritime setback from losses to established rival navies.