I spent quite a while as a fireman/paramedic. Long ago (mid to late 70s) I bought a flashlight called True Grit. It was a machined aluminum modular D cell body light made, I believe, here in Cleveland, Ohio. You could add or subtract body modules to go from 2D to however many you wanted and could find a lamp for. Mine is usually in 3D mode, but I have modules to go out to 6 if I want. The head is easily 3/8" thick in places, and ads showed it stopping a 38 caliber bullet. Everything was easily replaceable. Even the lanyard stud unscrewed and if you put it into the tailcap from the inside the end was smooth so it could stand on end. The tailcap, and all the modules for that matter, have very long threads so that you don't have to get them started against spring pressure when you are replacing batteries - something I wish everyone did, especially Mag.
The beam is not adjustable, and is a fairly tight spot. It went on a lot of calls with me, and broke out more than a few car windows and windshields. Mine is now pretty obviously a scarred veteran, but it still works just fine, and it's tempting to convert it to Luxeon. I've never seen another one though.