He later pursued his studies in Paris and briefly worked at the Ministry of Finance, but was interrupted by World War II and he served in the French Army.
By 1943, Jaeger also worked with the information service of the Francs-Tireurs et Partisans (FTP), the communist arm of the French Resistance.
The French Communist Party (PCF) put Jaeger in charge of Procinex, a corporation that would create short films for left-wing audiences and for the Soviet sphere of influence.
As these films were commissioned by a political party, they tended to aim more for the educational, inspirational, and/or propaganda style rather than as pure entertainment.
Jaeger obtained the approval of the Party to change Procinex into a more standard production company that would make money-making crowd pleasers.