Translate the following English sentence to French:
"It had been missing one instrument which was vital to the credibility of its commitment, i.e. the capacity to mobilise sufficient military resources to allow it to decide and act autonomously within the context of the so-called Petersberg tasks."
Il en manquait un, fondamental, pour assurer la crédibilité de son engagement, à savoir la capacité de mobiliser des moyens militaires suffisants pour lui permettre de décider et d'agir, de façon autonome, dans le cadre des missions dites "de Petersberg".