Group Attack
When launching an attack, there will be an option on your Fleet page called "Formation". If one is to click this, they will be given the option to send invites to themselves, their buddies, and their alliance. Anyone that accepts the message in their inbox will join in for the group attack.
If a invited party is further away than you, this will delay the time of the attack until the late arriving party would arrive. It is believed that anyone who would cause a delay of more than 30% of the original take will not be able to join.
Additionally, if you are not within attack rank range (ie too high of a rank or too low of a rank vs the person being attacked) you will not be accepted into the formation even after accepting the 'join attack' request. Check the colony being attacked first to see if you would 'normally' be able to attack before trying to join a formation... if you can not attack as an individual because of the difference in rank then you can not participate in the group attack either.
When the attack organizer recalls, the invitees will still attack. The attack simply changes from a group attack to a normal one. This guarantees that return times of the invitees will not be tampered with by a formation leader. Also, since the formation leader isn't 'locked in', he can recall to defend his base with out canceling the other players' attacks.
The offensive counterpart is Group Defend
