How in the world did the British figure those pancake helmets wee okay for combat. They kept the rain off your ears. That's it.
They weren't for "combat", they were to protect troops sheltering in trenches from the downward-directed shrapnel of shells exploding overhead, which was a comparatively new thing in warfare. The helmet had its drawbacks, but it entered service with a whole range of countries and stayed in service for a very long time. It was in US service until 1942.
