Sentinel is the name of the Axalon's automated defense system, it is not only regarded as extraordinarily effective but as perhaps too effective. To put it simply, most battles near the Maximal Base end by someone activating Sentinel. Understandably, the Maximal device is highly coveted by the Predacons.
The Sentinel System itself consists of an extremely powerful energy shield, and the simultaneous activation of every weapon attached to the Axalon, plus an array of internal defense systems. Despite its power, the shield can be disabled under unusually heavy fire.