https://en.wikipedia.org/wiki/Celtic_crossIt is suggested that adoption of the symbol in the context of right-wing politics is linked with the activity of Jesuit priest Paul Doncœur, a prominent figure of the interwar scout movement in France. In 1924, the victory of anti-clerical Cartel des Gauches in general elections caused the mobilisation of right-wing forces, with Doncœur playing a major role in formation of Fédération Nationale Catholique and Ligue DRAC. The same year, impressed by Quickborn, a Catholic organisation within the German Youth Movement, he founded its local equivalent, Cadets. Doncœur, inspired by the G. K. Chesterton's novel The Ball and the Cross, decided that the symbol of the movement, croix cadet, should consist of a circle, representing the material world, supported by a square Christian cross intersecting it.
After the Fall of France, Vichy government relied on pre-existing organisations to implement its youth policy according to the principles of the National Revolution. The field was dominated by Catholic scout movements, the leaders of which were put in charge of Secretariat-General of Youth. In 1941, the symbol of Doncœur, now named croix celtique, was adopted as an emblem for Cadets of the Légion in Algeria, a youth movement within Légion Française des Combattants, a veteran organisation which the government hoped could be transformed to function as the single party of the state. Then it was used as insignia of Equipes nationales, a youth civilian service institution founded in 1942. After the war, Pierre Sidos appropriated the symbol as an emblem of the far-right movement Jeune Nation, founded by him in 1949.