From 1926, he was serving in a field artillery regiment stationed in Livorno and at the same time was a teacher at the local Military Academy.

Marras, who soon became known for his courteous nature, also wrote numerous reports on the German armaments situation, paying particular attention to the Wehrmacht and the training of personnel in the war academies.

He gave an unusually accurate picture of the German war effort in terms of practical and pragmatic training, but also on human aspects and weaknesses such as pride and arrogance.

From July to November 1939, he was active in Rome and Libya and then transferred back to Berlin.

On 31 March 1944, the German authorities handed him over to the fascists of the Republic of Salò in northern Italy and since then he was imprisoned in Verona then Gavi and finally in Alexandria, but in August of that same year, he managed to escape to Switzerland.