Oh come on! There’s no way an army base can’t secure the vast majority of it’s weaponry from theft. Not even the massively overrated US military can fail at such a simple task. At most some small arms and most common ammunition might slip away. The only way this happens is with inside help. Corruption is endemic to anything the USA does geopolitically, and even to themselves.
Of course there’s also some smokescreen lies in there. DAESH/ISIS don’t have to steal anything from US troops. They were trained and armed by and are still protected by US forces. The only remaining terrorist groups of any scale, are inside areas controlled by illegally present US forces.