While the addition of various gimmicks to the central theme of "Robots in Disguise" was by no means new to the Transformers franchise by the time the Armada line came into being, Armada could be argued to be one of the first times that a play gimmick (that is, a gimmick featured around something the toys could do, as opposed to something the toys resembled, as with the Beast era) became a central theme than an entire line would be built around. In the case of Armada, this central theme was the introduction of the Mini-Con.
Featured in the Air Defense Mini-Con Team are three Mini-Cons. From left to right, these are Jetstorm, Runway, and Sonar. Since it's been a while since Mini-Cons have been featured here, I should say that Mini-Cons were tiny Transformers (roughly Micromaster sized) which could plug into larger Transformers to activate special features.
Every toy designed for the Armada line either was a Mini-Con, or included a Mini-Con with it. You could plug most Mini-Cons into specially-designed ports on the larger toys to unlock features like hidden missile launchers, or special claws, for example. There were a few exceptions. In some cases, the larger robot was designed with the Mini-Con that came with it specifically in mind. Mini-Cons sold separately, like these three, would not be able to unlock those particular gimmicks, but that still left a large amount of cross-compatibility available.
When Mini-Cons were sold independently of larger Transformers, they tended to come in three-packs such as this one (also, the previously-featured Street Action Mini-Con Team). Many of these three-packs (but not all) featured Mini-Cons that could not only activate the special features of larger toys like other Mini-Cons, but were themselves designed to combine with each other to form an accessory that could be used with the larger toys. In the case of the Air Defense Mini-Con Team, the three Mini-Cons combined to form the "Star Saber," which could be wielded by any Transformer with a 5 millimeter fist hole (which was increasingly the standard size for most Transformers at that time). Theoretically, the Star Saber was a powerful sword which could cut through anything, and having possession of it could tip the scales of power in the struggle between the Autobots and the Deceptions.
Unless, of course, the other side managed to get one of the other Mini-Con Team relics available. I'll feature one of these others next time.