'Jupiter' (iii) was a French undertaking to take the Ile d’Oléron, one of a group of German-held positions along the west coast of France including Brest, La Rochelle, Lorient, St Nazaire and the Gironde estuary, within 'Vénérable' (29 April/1 May 1945).

Transported and supported by Vice-amiral Joseph Rue’s naval force (heavy cruiser Duquesne, destroyers Fortuné, Alcyon and Basque, and a number of lighter units), French troops landed on the 67.2-sq mile (174-km²) island, which is 18.5 miles (30 km) long and possesses a maximum width of 5 miles (8 km), and took it from the Germans, whose last units surrendered on 1 May.

The Germans had occupied the Ile d’Oleron and nearby Ile de Ré in the summer of 1940, and began to fortify them in 1942. The Organisation 'Todt' construction apparatus built large number of pillboxes and bunkers, as well as sites for coastal artillery.

A first resistance group, led by Robert Etchebarne, was dismantled in October 1943, but with the arrival on the European continent of French forces the ​resistance effort was reconstituted with the aid of the Forces Françaises de l’Intérieur (French forces of the interior), which supplied the weapons and equipment which were needed. On the eve of 'Jupiter' (iii), the 'Pré-salé' (salt marsh) totalled some 200 men and women.

Desiring to open French ports for the supply of their forces landing in France from June 1944 in 'Overlord' and 'Dragoon' (i), the Allies considered as assault on the Ile d’Oleron, but felt that the gain would be unlikely to be worth the cost of an assault on Korvettenkapitän Werner Schaeffer’s 1,980-man garrison (including 200 Italians, 50 Poles and 40 Russians) manning a complex of 29 bunkers and 42 field fortifications shielded by 30,000 mines and supported by 180 pieces of artillery. After 'Vésuve' against Royan, Général de Corps d’Armée René Marie Edgar de Larminat, commanding the French forces on the nation’s Atlantic seaboard, decided to take the Ile d’Oleron in 'Jupiter' (iii). de Larminat’s forces included the 50^th and 157^th Régiments de Marche d’Infanterie, a number of marine units, and detachments of the local resistance forces.

As the vessels carrying the landing troops headed for the beaches of the Pointe de Gatseau, Capitaine Leclerc, head of the resistance movement on the island, organised sabotage on the mainland, and Lieutenant Schwartz, his deputy, managed to neutralise the mines in the entrance to the harbour of Boyardville.

Originally scheduled for 06.00 on 29 April, 'Jupiter' (iii) was postponed until 05.30 on the following day, when it was preceded by an artillery bombardment from French guns on the mainland. At 06.00 the first French pioneers landed on the Pointe d’Arceau and then other troops came ashore from a force of 24 landing craft. Within 30 minutes the French had established 700 men in their beach-head, and soon severed all possible links whereby the Germans could be reinforced from the mainland. The landing craft quickly established a ferry service from the mainland, and the beach-heads received additional men, vehicles (including four tanks), weapons and equipment as it started to expand.

The beach-head on the south-eastern end of the island was deemed secure by 07.00 and the landed troops started to move to the north-west, though progress was initially slow as the German minefields had first to be located and marked for avoidance or cleared. By 12.00 St Trojan les Bains had been liberated, and the French troops pressed forward to Le Château d’Oléron, which was liberated at 20.00. The French initial advance from the south-east was halted for the night, and during this pause a new landing was prepared for a descent on Perrotine, farther to the north on the island’s east coast near Boyardville.

Delivered at 01.00 on 1 May, the new landing was made by the Commando 'Fournier' of 207 French marine corps volunteers. The landing was unopposed, and the marines pressed inland to liberate Arceau and Les Allards by 05.00. The men from the two landings met shortly before 05.00, co-operated in the liberation of Dolus d’Oléron and then advanced to liberate La Lémigeasse and La Cotinière, on the island’s west coast, at about 12.00. During the afternoon the French forces continued their advance along the island’s length toward the north-west, and at 14.00 took the island’s main town, St Pierre d’Oléron. Chaucre, Chéray and St George d’Oléron were liberated at about 16.30, and St Denis d’Oléron and the Pointe de Chassiron on the island’s north-western tip at 18.00, when the German surrendered. The last two pockets of German resistance, in Boyardville and the dune area of Ford des Saumonards, fell a little later at about 22.00.

Of the 8,882 French troops who took part in the liberation of the island, 18 were killed and 55 wounded. The German garrison lost about 50 men killed and 60 wounded, the rest being taken prisoner.