Very old problem - a co worker of mine, Kevin Boland, who is now a VP at FN USA, but worked for Knights Armament after many tours in the Canadian army and then as a private contractor, came up with a solution for our NSN Acogs probably 16 years ago now. All the Dr. Optic red dot type sights you saw mounted on the top/back of Acogs were based on his original design/idea, and it worked well for giving you some CQB sighting capability with a fixed 3.5/4/higher powered optic.
The only problem was it was pretty high off the bore axis, but again, beats the back up sights on many Acog models.
If the Navy unit you're in won't let you mod your Acog sight yourself with such a mount/red dot, the only option IMO is to paint the backup front sight post on your Acog with some glow in the dark paint, and just use that built in sight on the top of the unit. Sucks, yes, but unless you can mount 45 degree angle irons on your rifle, or a dot on the Acog, it's really your only option.
So far as technique using that, it's the same as any iron/fixed/back up sighting system, most of your focus on the front post, and lots of repetition. Also, when using a shoulder supported weapon, there are CQB shooting techniques using unsighted fire at close ranges which are just another option in your tool box to have. Within CBQ distance you should be able to get reasonably decent hits with just point shooting with a rifle, although this isn't the optimal way to do it (dot sight of some kind being the best).
I have several of the older 1st gen Elcans as they were available here in Canada by the bucket as surplus sights with dying tritium inserts, Elcan always has made great glass. I sold my Specter years ago to fund a CQB Leupold scope, it wasn't cheap, in fact the Specter is one of the most expensive combat optics out there. Was the USN switching back to the Acog due to budget issues, or something performance related?
