The Buckler is a Loyalist Agrav first usable in the Campaign Mission, Fly Blackbird.
There are faster agravs out there, and there are more heavily armed agravs too, but few can do so much as well as the Buckler can. Airframe has mercifully few retrofits on its service record, the big Burham power plant keeping its big ass off the deck nicely, Mog-style indirect vision system keeps the pilot cocooned in titanium sheathed in ablative armor. Some pilots get a bit panicky in there, that's about the only thing you can say against it. It's got a log service life ahead of it.