With the French, 1940
On the outbreak of WWII the French recruited heavily from Republican refugees of the recently ended Civil War. The choice for these men was remain in French internment camps, or join the French army. The French took between 5,000 and 8,000 Republicans into the French Foreign Legion, and 10,000 went to the Infantry. In addition 55,000 Republicans were drafted into labour battalions, and at least some of these saw combat during the Fall of France (1940); English officers saw one Spanish labour battalion attack the advancing Germans with weapons seized from a fleeing French unit. During the course of the war Republicans fought in most theatres, for example at Narvik, in the raid on Brest, with the Long Range Desert Group, Leclerc's 2nd Armoured Division, the British SAS, and the French resistance.
French Resistance (maquisards)
Basque units fought with the French resistance, in particular the FFI (Forces Français à l'Intérieur), and in small guerilla bands in the Pyrenees.
Free French and La Nueve (RMT)
Javier Gomez and Cristóbal López sent information about Spaniards fighting with the French. They are part of a reenactment group for "La Nueve":
http://juanmario.rey.en.eresmas.net/indexnueve.htm
Spanish fought with the Free French Troops and in the F.F.I. Mostly all the Spaniards that fought the Free French Army were in the 13eme Demi Brigade de la Legion Etrengere and they fought in Narvik, Ethiopia, Syria, North Africa (Bir Hakeim), Italy, France and Germany.
The Spaniards that joined the Regiment de Marche du Tchad (RMT) fought in the Fezzan campaigns with General Leclerc and after in the Tunisian Campaign. After that, when the R.M.T. formed the Armoured Infantry Regiment of the 2eme. Division Blindee ("Leclerc's Division") they took part in the Normandy Campaign, they were the first allied troops to enter in Paris on August 24th (evening) and they fought in France and Germany ending the war in Berchtesgaden.
In particular ex-republicans formed the 9th company in the RMT (
9ème compagnie de combat du RMT) - they called themselves "La Nueve". The First and Second Platoon were formed from moderate Socialists and Republicans, whereas Third Platoon comprised Anarchists. There were few Communists. This unit fought from Normandy to Germany. "La Nueve" wore standard USA Uniforms (M-41 Jacket, HBT Coveralls, OD wool shirts and trousers, service shoes, dismounted leggins, M-36 suspenders, etc. Usually they didn't use tanker and M-43 jackets but could). In combat they wore the M-1 US standard helmet but they used as a garrison cup the French Colonial Infantry "Bonet de police" or "calot" cup in the tradicional colours (Blue with red pipeing) and with a golden anchor in the left side. As well, they wore French insignia (normally they wore 3 french insignias : the "2nd Armoured Division" shield, the "Free France Army Moustique" and the "Regiment de Marche du Tchad" insignia) and grades. Veterans say that some Spanish soldiers wore a small Spanish Republican flag up in the left arm (where the G.I.'s wore the unit pacth). These practice was unauthorized by the French Army rules but Officers let men to wore it. Anyway, I've never seen this flag in any IIWW pictures from "La Nueve".
Basques at Normandy
Basque units - probably sailors - saw service alongside Allied units at the Normandy landings on D-Day.