Teribus,
One minor correction, ont steel helmets
"...they were not universally issued to British troops until late 1915/early 1916..."
The issue began in 1916 and, until the middle of the year they were issued as "trench stores" (along with such materials as barbed wire, flares, grenades, duckboards and the like, the outgoing unit left them behind and the incoming unit took them over. The supply only reached the level to allow "universal issue" just before the opening of the Battle of the Somme in July.
Walrus