'Myrmidon' was a British uncompleted special forces plan to attack targets in Bayonne, on the confluence of the Adour and Nive rivers, at the southern end of German-occupied France’s west coast close to the frontier with Spain, in conjunction with the 'Chariot' attack on St Nazaire in German-occupied France (5 March 1942).

The object of this undertaking was to cause disruption of the road and rail transport between France and Spain by landing some 3,000 troops (Nos 1 and 6 Commandos), who would then be supplemented by one and a half Royal Marine battalions along with one armoured regiment and one motor battalion.

After embarking on the transport ships Queen Emma and Prinses Beatrix, the force spent a month sailing off the French coast disguised as Spanish merchant ships. On 5 April the ships approached the mouth of the estuary in order to carry out the landing despite the adversity of the weather, but then encountered an uncharted and therefore unexpected sandbar and, unable to cross it, returned to the UK as the raid was called off.