On 7 September 1907, Painvin was appointed reserve second lieutenant and assigned to the 33rd Artillery Regiment to attend his third year on obligatory military service.

On 21 January 1915, Painvin proposed a method, the ARC system, which made it possible to discover the cryptographic key used for the encryption and this with a single text.

One path of encrypted diplomatic communications in particular, led to the unravelling of the spy Mata-Hari; during the first months of the war, Painvin's work made it possible to quickly follow the evolution of this enemy figure.

In June 1918, the German Imperial Army was preparing for a final push on the Western Front to cover the 100 kilometres (62 miles) that separated it from Paris.

After some 26 hours of intensive work, until he was physically exhausted, he succeeded in reconstructing the grid and permutation used for the encryption and was able to decipher the intercepted message on 2 June 1918.

The message was immediately forwarded to Marshal Ferdinand Foch's French headquarters and convinced him that the Germans were planning a massive attack in the section of the front at Compiègne.

Foch concentrated his last reserve troops around this city, which meant that the German attack that took place here shortly afterwards could be repulsed.

Breaking the German ADFGVX cipher took its toll on Painvin's physical and mental health and shortly after the message was delivered, he collapsed, exhausted by all his efforts.

He would, however, not be able to disclose or talk about his work accomplishments for a large part of his later lifetime, because the activities of a number of French government services were under cover of military secrecy from the general public until 1962.

The inventor of the ADFGX/ADFGVX cipher, the German signal corps officer Lieutenant Fritz Nebel [de], did not learn of Painvin's achievement until 1967.

In 1966, nearly fifty years later, Fritz Nebel learned that his system had been broken during World War I and said that he had originally proposed a double column transposition as the second stage of his method.

However, his proposal was rejected in discussions by his superiors and, for practical reasons, they decided in favor of a (cryptographically significantly weaker) simple column transposition.

The company mobilised new methods of electrochemistry to produce on a large scale the first stainless steels at affordable prices, helped by the French inventor and industrialist René Marie Victor Perrin (1893-1966), who developed the Ugine-Perrin process.

The company would remain at the cutting edge of technology 40 years later with the inauguration of the giant Fos-sur-Mer steel plant near the Rhône.