M51 OTAN model, with an inner plastic liner and webbing cover, plus a locally designed chinstrap system. It was supplemented, but not fully replaced, during the 1980's by an Israeli composite helmet.
The US Army began to replace its M1 steel helmet with the PASGT composite helmet during the 1980's. Since then it's been through a second and third generation of composite combat helmets, with a brand-new fourth-generation helmet just coming online to replace them.
I'd heard that the current-issue US Enhanced Combat Helmet was a pretty good product, but I've always been a bit dubious about bullet resistance claims. I've seen too many dead soldiers! Nevertheless, its performance has just been illustrated in very emphatic fashion.
Staff Sgt. Bryan McQueen was nearing the end of his tour in Afghanistan with the 1st Security Forces Assistance Brigade on Sept. 3, 2018. He, his fellow soldiers and nearly 50 Afghans were headed to a security meeting, as routine as any other daily assignment.
Machine gun fire erupted.
McQueen felt what he could later only describe as a horse kick to the back of his head and he fell flat to the ground, landing on his face.
But in seconds he was on his feet with a simple question.
“Did these (expletive deleted) really just shoot me in the head?” he said.
. . .
The 7.62x54mmR round from the truck-mounted machine gun struck the back of McQueen’s helmet, shredding some of the materials but not penetrating the shell.
This week that same helmet, bisected and mounted on a plaque with McQueen’s name and the appropriate unit coinage, was presented to him here at a Personal Protective Equipment soldier return ceremony.
The force of the round did cause a minor brain bleed but no permanent damage.
There's more at the link.
That's impressive! The Russian 7.62x54mmR round is the ballistic equivalent of the US .30-06 Springfield or NATO's 7.62x51mm. It takes a lot to stop one of them in its tracks like that. Steel helmets usually won't do more than slow them down a little. I can think of several former comrades-in-arms who would have been very grateful for one of those helmets, way back when . . .
If the new Integrated Head Protection System helmet does, indeed, offer "100 percent greater protection against head trauma injuries" over present-generation helmets, it'll be something very special. I hope it works as advertised.