 Complete the following phrase:  The construction of Fort Chaberton on an even higher peak on the Italian side of the frontier rendered the Fort de lOlive vulnerable to artillery from Chaberton, which was higher. The position was used by the French Army in the defense of Briançon until 1940, when it was part of the Fortified Sector of the Dauphiné. The fort took artillery fire from Chaberton during the 