When I joined the Army, apart from dress headgear, we had to wear a beret, and new, on issue, they were as flat as dinner plate and looked ridiculous, so the thing was to “shrink” them to fit your head and sit properly on it. This involved soaking them in warm water, pummelling them a bit, shaping them to your head, and then leaving them to dry. This was actually a forbidden practice and if they weren’t completely dry when required to be worn, the leather they were edged with would leave a dark tell tale mark around your forehead and get you into trouble!