ACH (Advanced Combat Helmet) helmets were derived from MICH (Modular Integrated Communications Helmet) Helmets, the result of a late 1990’s project to develop the next generation of helmets to replace the older PASGT designs from the 1980’s. These were the primary US service helmet during the 2000’s. MICH helmets were first developed in 1997 (source: https://web.archive.org/web/20180104112023/http://www.natick.army.mil/about/pao/pubs/warrior/00/novdec/kevlar.htm) with earliest helmets are dating to 1998 (source: https://www.iraqimilitaria.com/mich-helmets), and were referred to as “TC-2000” helmets for full cut designs, “TC-2002” for mid cut, and “TC-2001” for high cut (source: https://soldiersystems.net/2012/08/18/canipe-correspondence-helmets-state-art-then-now/). This page will mainly focus on full cut helmets, though some have been modified by end users to other cuts, much like what was done to the Afghan PASGT helmet by the APU.
The MICH was meant to combine the ballistic protection of the PASGT with the comfort and improved visibility of various non-ballistic bump helmets Special Forces operators sometimes used (source: https://pubmed.ncbi.nlm.nih.gov/25077182/).
ACH helmets were procured starting in 2003 (source: https://www.sciencedirect.com/science/article/abs/pii/S1359836822002694) and are largely the same as the MICH helmets they are derived from. The ACH is still used as of December 2022, though it has been getting replaced by the Enhanced Combat Helmet (ECH, source: https://en.wikipedia.org/wiki/Enhanced_Combat_Helmet_(United_States)).
For further information on modern US Kevlar Helmets, see https://www.iraqimilitaria.com/a-guide-to-us-kevlar-helmets.
Army Ranger (2010):
Helmet had velcro on side at one point. There is also evidence of camouflage paint and field use.
Inside:
“Suspension” system is actually foam pads.
Labels:
Near top of helmet. 
On left side of ear (as worn).
2010 date.
Usage Photos:
November 23, 2006: A Ranger with 2nd Bn., 75th Ranger Regiment, provides overwatch security on an objective during a day-time mission in Iraq (from https://commons.wikimedia.org/wiki/File:U.S._Army_Ranger,_2nd_Battalion,_75th_Ranger_Regiment_providing_Overwatch_in_Iraq_2006.jpg). Note Orc Industries PCU L5 jacket. 
A US Army Ranger takes aims with a SR-25 Mk 11 Mod 0 sniper rifle. The Mk11 is a 7.62mmx51mm caliber weapons system designed for medium range sniping (from https://www.americanspecialops.com/photos/rangers/ranger-sr-25.php). 
US Army Rangers pictured during operations in an urban environment (from https://www.americanspecialops.com/photos/rangers/rangers-street.php). 
Circa 2006: US Army Ranger in Iraq (photo from https://twitter.com/tacticalporn/status/1031676656149311488/photo/1). Note Ranger-modified DCU jacket and RLCS gear (basis for date).
Navy TC-2000 (Training Use?, 2008):
Velcro hook on back is meant to hold goggle strap in place. 
Numbers stenciled onto tape indicates some kind of training use since they would be used to identify trainees.
Inside:
Front night vision shroud holes were drilled from the factory (velcro hook pads cut around holes).
Labels:
2008 date like all Navy TC-2000 helmets (source: https://www.iraqimilitaria.com/mich-helmets).
Buckle:
Also has a 2008 date.
Helmet Cord Attachment:
This formerly elastic “bungee” cord was meant to be used with the night vision goggle mount’s arm.
Usage Photo:
