Armour worn by First World War tank crews as protection from armour splinters

This piece of armour, which looks like the kit of a Chatlanian, was worn during the First World War. And it is only part of a tank crewman's full equipment, which also included a proper chain-mail coat. Why tank crews in particular? Without such armour, under machine-gun fire the entire crew of a tank would have been turned into mincemeat: imagine that the armour of the first tanks flaked away on the inside and struck the crew like shrapnel.