In the March, 1943 edition of the US Army’s Intelligence Bulletin, a short article discusses a British study of combat head injuries and the protection afforded by various styles of steel helmet.
The article refers to a report written by a British medical officer serving in North Africa. The officer examined 150 cases of localised skull fractures, 90% of which occurred during fighting in the Western Desert (Egypt and Libya). The majority of the head wounds were believed to have been caused by shell and grenade fragments.
British troops wearing the old pattern and the new MkIII helmets during fighting in Caen in 1944 (source)
The report showed that a considerable portion of the skull was not protected by the Brodie helmet worn by British troops (and until 1941, by the US). With a large number of fractures being reported on the forehead and above the ears. The diagram above shows how the older Brodie helmet, developed during World War One failed to protect a significant proportion of the skull.
The diagram shows the outline of the old British helmet and the new proposed helmet, the MkIII, which had been developed in the early 1940s, as a result of the earlier helmet’s inadequacies, but was only introduced in 1944. It also shows the outline of the new US M1 helmet, which appears to provide the best protection of the three.
Military Reports on United Nations, No.2, 15 January 1943, Military Intelligence Division, War Department, pp.34-5