Pierre Clavel begins his career in aviation during the First World War. Engaged first of all as artillerist, he asks to be transferred in aviation. He is affected as pilot with the flotilla SPAD XX. The function of these two-seaters comprising a pilot and an observer was to regulate the artillery shootings to the top and inside the enemy lines what involved aerial combats in the event of meetings with the adversary.

After the war, he proposes his services with the Air-mail Ligne Latécoère which has been just created. In 1921 it returns under the orders of Didier Dorat to Toulouse. Then this last assigns it to Alicante like person in charge of this Aéroplace. The daily routing of the mail must be done by all times. Sailing at sight of ground, only a watch indicating the duration of autonomy of the gasoline tank, the pilot and the mechanic are welded in the same adventure. When it leaves the Line with regret, in 1924, it continues to be involved on new apparatuses as reserve officer.

With the declaration of war 1939/40 it engages at the time of the countryside of France. It is indicated to order the Battalion of air 109 in Tour as instructor of a Fighter squadron. Thus its course in aviation during is completed which its control, so much on the human plan than within the framework of the missions which are entrusted to him, are worth to him the Military Cross and the Légion of honor on a purely military basis as well as a foreign medal the cross of the Christ of Portugal.