The helmet has 10198 inside but I cannot find that on any of the usual part databases. Does anyone have any ideas?
It's probably a 3rd-party LEGO-compatible accessory, several 3rd-parties make such military themed accessories.
LEGO doesn't make very many modern-day military-themed pieces and I found similar pieces on one 3rd-party accessory shop. It's not an exact match, but it's pretty close. It might be that you have an older version of their product, or some competitor's product.