Here's the trick. Go to: http://dodpki.c3pki.chamb.disa.mil/rootca.html
Then it will say this silly message about you "not using a supported web browser", and will not display the cert links. No problem, just *View Source* (hit Ctrl+U). Once in the source, you'll see links to four *.p7b files, conveniently turned into real links by Chrome. Download all four to a directory of your choosing.
Then, from a terminal, cd to the directory, then run:
for n in *.p7b; do certutil -d sql:$HOME/.pki/nssdb -A -t TC -n $n -i $n; done
You don't have to restart Chrome or anything else. It should immediately start working, and you can test it by looking for the green https in the URL bar for DoD web sites (such as https://www.us.army.mil ). Also, you do not get annoying certificate warnings. Also, the following should show the results of your cert import:
certutil -d sql:$HOME/.pki/nssdb/ -L
Once you're in...(Edit)
You'll probably be interested in Logging in to AKO Webmail with Google Chrome on Linux.