Assault Frigates (often referred to in-game as AF's) are T2 frigates
. They have extremely high resistances and due to there small size become quite a challenge for any ship using High calibur weapons to hit.
These ships may enter any dead-space complex that a frigate can but are much much more versatile and tougher than any T1 frigate. While not as fast as an InterceptorFrigate
these ships are a lot tougher and able to stand quite a beating from bigger ships. With the proper configuration it is quite possible to tank and destroy a NPC Battleship spawn without taking any significant damage. You should be prepaired to use a significant amount of ammo to pop a NPC Battleship though. An AF with the proper equipment should be able to easily take any lv 2 mission and some lv 3's depending upon your skills and equipment preparation.
An AF is a good stepping stone from ShiptypeCruiser
and will serve any pilot well to acquire.