When a fleet or colony is being attacked, if it is being overpowered it will send out a distress call to nearby
fleets for assistance. A colony will always send a distress call at the start of a battle, however many times the colony's
ground defense is smashed before friendly fleets can show up to help. Any fleets that have standing orders to answer distress calls will
transfer to the battle location and
support the fleet or colony that made the call.
It must be noted, however, that distress calls made by a fleet at the entrance to a system usually need to be repeated multiple times before they are answered - and they are sometimes not answered at all.
Only fleets that are within 60,000km * their scanner level will automatically answer support / distress calls. This range is halved for calls in local space and the calls do not exit or enter systems.