Group Defend

Group Defend lends your ships to somebody else. You send a fleet to an alliance mate's or a buddy's planet, moon or Hephaestus Class Attack Platform, it sits in orbit for as long as you paid for, and it fights alongside whatever the owner has parked there. It is the defensive twin of Group Attack.

You can only defend a planet that belongs to someone in your alliance or on your buddy list. You cannot Group Defend your own planets. Moving ships between your own planets is Deploy.

Sending defenders

Open the Galaxy page and look at the Actions column. Ally and buddy planets get an extra shield icon labelled Defend. Only they get it, so the shield is a quick way to spot who you are allowed to help.

The same mission is on the Fleets page as well. Pick Group Defend under Mission, type the coordinates, choose your ships and send it. Both routes open the same window.

Three things to set:

Ships. Anything that flies. Solar satellites cannot be sent because they have no engines, and a defend fleet carries no cargo.
Speed. Same 5% to 100% slider as any other mission. If nothing is inbound yet, a slower flight saves a lot of hydrogen.
Defend Hours. Whole hours, 1 to 24. This is how long the fleet stays in orbit once it lands.

Hit Dispatch Defenders and the fleet leaves.

What it costs

Two bills, both charged at launch. First the normal flight hydrogen for the distance and speed. Then hover fuel, which is a flat rate per ship for every hour you asked the fleet to stay.

Ship	Hydrogen per hour
Atlas Class Cargo	1
Artemis Class Fighter	2
Carmanor Class Cargo	4
Hercules Class Cargo	5
Apollo Class Fighter	7
Hades Class Battleship	25
Poseidon Class Cruiser	30
Dionysus Class Recycler	30
Zagreus Class Recycler	40
Athena Class Battleship	50
Ares Class Bomber	100
Prometheus Class Destroyer	100
Gaia Class Colony Ship	100
Hermes Class Probe	0
Shadow Probe	0
Zeus Class	0
Hephaestus Class Attack Platform	45,000

For most ships that works out to a tenth of the ship's fuel rating per hour. Two do not follow the rule: an Apollo is 7 rather than 7.5, and a Carmanor is 4 rather than 12, which makes the Carmanor by far the cheapest thing to leave sitting anywhere. Probes and the Zeus round down to nothing, so parking probes costs only the flight.

A simple case: 10 Hades for 1 hour is 10 x 25 = 250 hydrogen of hover fuel on top of the flight. The fleet in the screenshot above (40 Prometheus, 20 Hades, 60 Athena, 120 Poseidon) burns 11,100 an hour, so 6 hours came to 66,600 hover fuel, and 76,973 hydrogen once the flight was added.

The whole amount comes out of the origin planet the moment the fleet launches. None of it is ever refunded, including the hover fuel for hours you did not end up using. The trip home costs nothing extra.

A defend mission uses one fleet slot, and it holds that slot for the flight out, the whole time in orbit, and the flight back.

Limits

Six defending fleets per planetoid. Fleets still on their way count against the six. Add the owner's own ships and that is seven fleets on the defending side, matching the seven a Group Attack can bring.
Six fleets, not six players. One player can fill more than one of the slots by sending from more than one planet.
A planet and its moon are separate targets, and each gets its own six.
Deployed platforms can be defended with normal ships. A Hephaestus cannot reinforce another deployed platform, and only one Hephaestus can be defending any one planet at a time.
A platform in transit cannot send defenders. Dock it or let it finish the move first.
A planet that just paid to move cannot Group Defend for 24 hours. The moon that moved with it is stuck too.
PVE Mode blocks it. While PVE Mode is on you cannot send defenders to another player. You are unattackable, so lending your fleet to somebody else's PvP fight would be a one way trade.
Nobody can reinforce a player on vacation. Their planets are sealed.
Newbie Protection does not restrict Group Defend. A brand new player can send help, and can receive it, even where an attack between the same two players would be refused.

The timer and recall

The clock starts when the fleet lands, not when it launches. On the Fleets page the row reads Group Defend on the way out, switches to Defending and counts down the hours you bought, then reads Defend Return on the trip home.

The red Recall button is on your Fleets page, and only yours. The player you are defending can see the fleet sitting on their own Fleets page but cannot send it home.

Recall while it is still flying out and it turns around on the spot. The trip home takes as long as it has already been in the air.
Recall while it is in orbit and it starts for home immediately.
You cannot add hours. If you want longer, recall and send again, and you pay the flight and the hover fuel again.

When the fleet gets home you get a Defend Return report listing what came back.

In battle

While the fleet is in orbit it joins the defence against every attack that lands on that planetoid. That includes attacks launched by your own alliance mates and buddies, and attacks launched by you.

The whole defending side fights at the group's best techs. Weapons, Shield and Armor are taken as the highest level among the planet owner and every defending fleet, and every ship on that side uses them. One well researched player joining a defence lifts everyone. Group Attack works the same way on the other side.
Losses are split by what you brought. For each ship type the game works out how many of that type each side had before the battle and shares the kills out in proportion. You do not eat somebody else's losses.
Survivors stay. A battle does not send a defend fleet home. Whatever lives through it keeps orbiting until the timer runs out or you recall it, and it fights the next wave too.
A fleet wiped out does not come home, and it never files a return report.
Everyone on the defending side gets the report, with a separate forces and losses block per player, so you can see exactly what your ships did.

Destroyed Ships Points are split by fleet value. In the report above the defending fleet was worth far more than the owner's home ships, so it took the larger share.
No points if you are on both sides. A player who is attacking a planet and defending it at the same time earns zero from that battle. The forfeited share goes to the other genuine players on that side.
Destroyed defenders leave debris in the target's slot, exactly like the owner's ships, and it counts toward the moon roll.
Your resources are safe. A defend fleet carries no cargo and is never plundered. Only the planet owner's stored resources are at risk.
Defenders do nothing against missiles. An IPM strike only hits defences. Your ships are neither a shield nor a target.

What an attacker can see

Your arrival is visible. Landing a defence fleet sets the defended planet's activity marker, exactly as any other arriving fleet does, so anyone looking at that solar system sees (*) beside the planet for the next 15 minutes and a minute count until the hour is up. It does not announce that a defence landed, only that something happened there, but a raider watching a quiet planet will notice. If you are covering a specific attack, land well ahead of it or accept that the arrival can be seen.

Past that, a spy probe is the only way to count the ships. Defending ships are folded into the planet's fleet list in the espionage report, mixed in with the owner's ships and not marked as visitors.

That report understates the defence in two ways worth knowing about:

The Technologies section only ever shows the planet owner's levels. It says nothing about the defenders' research, and the battle runs on the best in the group. A quiet planet with a heavyweight friend in orbit hits much harder than the report suggests.
It is a snapshot. A fleet that lands after the probe does not appear anywhere.

Hovering ships also push up the counterespionage roll, so a defended planet swats more probes than a bare one.

The Oracle does not help here. In SFC2 it sweeps solar systems for targets and reports who is where and how big they are. It does not show fleets in flight or in orbit, so it will never tell you a planet is being defended.

What you can see as a defender

Not much. Sitting in someone's orbit gives you no view of their incoming attacks, probes on them, or the other fleets defending alongside you. You get battle reports and the return report, and that is it. If you want to know what is coming, ask the owner.

Quest

Bringing one defend fleet home completes Hold the Line, worth 2,000 ore, 24,200 crystal and 1,800 hydrogen. See Quests. A defend fleet that is destroyed does not count, since the counter only ticks when the ships land back home.