Here’s another site that has a bunch of Army, Marine, Air Force, Navy, even Forest Service and Highway Administration as well as a variety of other manuals. If you go back to his main page he’s got pdf firearms manuals for almost every firearm out there too. http://stevespages.com/page7c.htm
As you noted, some manuals on the AKO server are protected and require a client-side SSL certificate. If you are Army, your PC will present the certificate to the server when it’s requested. If not, you can’t access the manuals at all.
They are all available at this web location, however, including the ones on “Intelligence Operations”, “Counterintelligence”, “Special Forces Operations”, etc.