Group Defend

You can send forces to help your allies and buddies defend their world. On the Galaxy page look for the chain link icon on the right side of the screen under the Actions Column. Selecting that will pull up an "Choose Ships for Fleet" window in which you can select the size of the force you wish to send as aid. You can also select how long that fleet will patrol your friend before moving back home, as well as how quickly the fleet will fly there and back - if an attack is not imminent then selecting a slower fleet speed could save hydrogen fuel.

From your own fleet menu you can also recall that fleet at any time.

This is the defensive counterpart to Group Attack