After his return from military service, Colonel Behn co-founded the Puerto Rico Telephone Company, which eventually spawned ITT.

Antony C. Sutton, in his book Wall Street and the Rise of Hitler, makes the claim that ITT subsidiaries made cash payments to SS leader Heinrich Himmler.

[3] Sosthenes Behn met with Hitler on August 3, 1933, and in 1936 there was a high-level meeting in Berlin, where it was proposed that Behn through ITT gain 50% of Focke-Wulf and oust Café HAG completely; however, after Barbara Goette intervened with Hitler, Ludwig Roselius's life was spared, he became the largest shareholder in Focke-Wulf with 46%, and a massive capital injection occurred.

These included a minority share in airplane manufacturer Focke-Wulf, which ITT had acquired through its contacts with German financier Kurt Baron von Schröder.

After Pearl Harbor, at meetings with Baron Kurt von Schröder and Behn in Switzerland, Westrick nervously admitted he had run into a problem.

Wilhelm Ohnesorge, the elderly minister in charge of post offices, who was one of the first fifty Nazi Party members, was strongly opposed to ITT's German companies continuing to function under New York management in time of war.

In 1943, ITT became the largest shareholder of Focke-Wulf Flugzeugbau GmbH with 29% due to Ludwig Roselius's Kaffee HAG share falling to 27% after he died on May 15.

In 1928, following the advice of Paul Janet, a physicist and member of the French Academy of Sciences, he, together with his brother Hernand, acquired the former property of André-Marie Ampère in Poleymieux-au-Mont-d'Or near Lyon, which had just been put up for sale.