I was trying to make up for being off-line for a week, lol…
There have been GOBS of flight helmets used by the US Armed Services since the begining of aviators having heads to cover… There’re a number of books on the subject of US military flight helmets as well as numerous sites that sell standard and custom painted HGU-55 and -33 helmets, one of the better ones being here:
http://www.customflighthelmets.com/paint.htm
http://www.customflighthelmets.com/tape.htm
http://www.customflighthelmets.com/paint.htm
Couple of the better books:
http://www.amazon.com/Vintage-Flying-Helmets-Aviation-Headgear/dp/0887407765
http://www.amazon.com/Jet-Age-Flight-Helmets-Aviation/dp/0764300709
The Navy/Marines shared flight helmets, the Air Force, not so much for most of last 50 years… Helicopter crews had their own, and the Army 's often differed from Marines/Navy as well, however there certainly was overlap… As for how many different types of helmets since WW2? Man, I don’t know for sure, but off the top of my head I think of at least 15, split amongst the three main branches with fixed-wing aircraft… The actual number is probably closer to thirty…
Some helmets were specific to the aircraft types, others for general crew wear, still others for FACs and sling-wing crews… During the Korean War, for example, Navy/Marine fighter pilots flew with a cloth helmet that had a hard shell snapped to it, USAF jet fighter pilots had one style of “hardhat”, while the P-51D pilots flew with the leather A-11s, but turn around and F-80 and F-82 pilots were wearing the same thing…
During the 60s and through the 80s there were no less than 10 different helmets in use by the four branches… It’s a b*tch keeping up with 'em all…