When Avions Marcel Bloch became the SNCASO, he joined the prototype team and, in 1939, flew his first prototype aircraft, the Bloch 175.
In 1940, he flew 15 missions for the Défense Aérienne du Territoire (Territorial Air Defense) as reserve second lieutenant in a defense squadron based in Mérignac. In 1941, his undercover activities obliged him to move into the free zone, where he joined a small core of the SNCASO that had set itself up in Cannes. Here, he flew the test flights of the SO 80, a small twin-engine postal aircraft built in the Bocca factory, as well as the SOP I, the first metal glider designed by Lucien Servanty. He also continued the test flights of the MB and the SO 161 (which became the Languedoc 161).
In 1942, when the free zone was no longer safe for him, he tried, unsuccessfully, to fly to North Africa with the SO 161. He did manage to reach Spain, but was captured and imprisoned first in the concentration camp of Miranda, then in Jaraba, from where he escaped at the same time as Henri Deplante. He subsequently made it to Gibraltar and then England in May 1943.
He was assigned to the Groupe de Chasse Alsace des Forces Aériennes Françaises Libres (Alsace Fighter Group of the Free French Air Force), but was called back to Paris in 1944 by Lucien Servanty to be Chief Pilot of the SNCASO. In 1945, Daniel Rastel made the maiden flights of the SO 30N and the SO 30R. He also flew test flights on Languedoc SO 161, MB 174, SO 3050 and SO 90.