Long War - Base Defense, March 2017

The hardest mission in the game.

This mission can be brutal, even when it goes well. Its also completely different than every other mission in the game and so it deserves special consideration. I am primarily going to discuss how to prepare and handle a base defense that happens in the late game; specifically March of the 2nd year, 2017. This is because I haven’t had a base defense mission occur before then in quite some time.

---

Triggering a Base Defense

The base defense mission is triggered when the aliens have reached Threat Level 4 and Resource Level 3+ for 3 months total.¹ On the next month, they will attack XCOM HQ. If the Base Defense has not occurred by March 2017, it will happen in that month, and that is typically, when I will encounter this mission.

First they will send a Battleship to shoot down the satellite over your HQ. If you have a spare satellite on hand you can immediately launch it, and then you may see the Assault Carrier heading for your base, which will initiate the mission.

If you have a couple Firestorms with plasma cannons, it is possible to prevent the Base Defense mission by shooting down this incoming Assault Carrier. But where is the fun in that?

---

Soldier Selection

Instead of choosing which soldiers will go on the mission, we pick 12 candidates that will be chosen at random. This creates some gear shortages. It is a good idea to know what soldier classes you intend to bring, and then buy extra gear to adequately suit all 12 soldiers in your soldier pool.

Typically I will try to have 7-8 MECs for this mission. By March, I usually have at least 8 MEC soldiers but only 3 sets of MEC gear. This means I need to build an additional 4-5 sets of gear, which consist of a MEC-1 suit, laser lance, scope, core armoring, and restorative mist. This is a huge expense. After refunds, 5 sets of MEC gear cost: $1335, 115 elerium, 145 alloy, 270 meld. The meld is the highest cost, and can be mitigated by dropping the restorative mist. It is definitely worth this expense, supposing you have the resources.

In my most recent campaign I had 7 MECs ready to go, and 4 were selected to go on the mission, along with a Medic and a Scout; a very lucky draw. After crunching some numbers I found that you really want 8 MECs in the soldier pool to insure a high number make it onto the mission. Here are the probabilities for each outcome, given the initial ratio of MEC/BIO in the soldier pool.

                 Soldier Pool Probabilities 
Soldiers
Selected        7-MEC/5-BIO          8-MEC/4-BIO 
6 MEC 0 BIO        0.76 %               3.03 %
5 MEC 1 BIO       11.36 %              24.24 %
4 MEC 2 BIO       37.88 %              45.45 %
3 MEC 3 BIO       37.88 %              24.24 %
2 MEC 4 BIO       11.36 %               3.03 %
1 MEC 5 BIO        0.76 %               0.00 %

Given the probabilities above, I think it is ideal to have a pool that consists of 8 MECs and 4 bio soldiers. Here is my ideal soldier pool:

MEC - Pathfinder
MEC - Pathfinder
MEC - Pathfinder
MEC - Shogun
MEC - Shogun
MEC - Valkyrie
MEC - Pathfinder / Jaeger
MEC - Pathfinder / Marauder
BIO - Gunner
BIO - Scout 
BIO - Sniper
BIO - Medic / Infantry / Assault

With this soldier pool there is a 97% chance to have at least 3 MECs on the squad, and 70% of the time there will be a 4/2 or 3/3 MEC/BIO split. This is great. With 7 MECs in the pool there will be an 88% chance to have at least 3 MECs. Having that many MECs will make the mission much easier. Another huge advantage is that when there are fewer bio soldiers in the pool you should not have duplicates of any of the bio classes, making the squad more efficient, and allowing you to select the best soldier of each class, and to give them the best weapon. Even when you end up with 3 bio soldiers, they will be the best bio soldiers you could ask for.

If you have fewer MECs in the pool you will need to choose more bio soldiers to fill in the gap. It is good idea to have one medic and one assault, but after that, additional bio soldiers should probably be shooters. Rocketeers run out of explosives too quickly; same with Engineers, unless you have Tactical Rigging. If you take an engineer, you may want to drop the medic, as both of those classes have limited offensive capabilities. I prefer a medic over an engineer.

You want to imagine the worst possible draw for the soldier pool you are considering, and then make changes to avoid that outcome. Prior to an ill-fated base defense mission, I decided upon a soldier pool that had 2 ITZ snipers and a Jaeger. All 3 were selected and it was a total disaster. ITZ conflicts with itself, and so it is ideal to have only 1 soldier with ITZ; 2 is probably fine; 3 is terrible. I assumed the probability that I would draw all three of those soldiers was extremely low, but it is actually about 9%, much higher than I had expected. The odds of getting any 2 specific soldiers is about 23%, also much higher than I would expect. Now that I know the odds, I won’t make that mistake again. There should be absolutely no incompatibilities in the soldier pool, period.

---

Base Mission Tactics

You start the mission with 5 random soldiers from your pool, and are immediately reinforced on the 2nd turn with another soldier from your pool, and 2 blueshirts. Twice more your squad can receive reinforcements when soldiers die, but this will never put your squad over the limit of 6 veterans, and 2 blueshirts. If only a blueshirt dies, then the reinforcement will have one blueshirt. To get the maximum amount of soldiers in a reinforcement, your squad would need to lose a veteran, and both blueshirts on the same turn. This means that it is a good idea to not use your blueshirts as target dummies for the aliens. Keep all your soldiers alive, even the blueshirts, until you really need someone to tank shots for the team. It is also better to take casualties in bunches, rather than one at a time.

The number of enemies is probably dependent on the month in which the mission occurs. In October of 2016 I have seen 31 enemies. In March 2017; 37. The difficulty level may also be a factor, and other players have reported seeing different numbers. In spite of these differences, the drop-in schedule always follows the same general pattern.

Here is the drop-in schedule for March, 2017²:

1st wave: 6 Command Center, 1 Rear Guard Station, 1 MEC Bay
2nd wave: 3 MEC Bay (usually mutons and chryssalids)
 -No Drop Round-
3rd wave: 8 Rear Guard Station (flyers)
 -No Drop Round-
4th wave: 6 MEC Bay (usually mutons and berserkers)
 -No Drop Round-
5th wave: 3 MEC Bay (further away - usually chryssalids)
 -No Drop Round-
6th wave: 5 Forward Access Tunnels (2 drones + heavy hitters)
7th wave: 4 Forward Access Tunnels (heavy hitters)

The first wave will usually have 3 very tough enemies, such as berserkers or mechtoids, but they are right out in the open, and your squad should be ready for them. If you can’t clear the Command Center of the most dangerous enemies, it is a bad sign.

After the 1st wave, you can move your squad to the MEC Bay, and easily dispatch the 2nd wave of drop-ins, or you can move your squad to the Rear Guard Station to set up for the larger 3rd wave of flyers. If you go to the MEC Bay, you will not be able to reach the Rear Guard Station before the 3rd wave lands.

On my current campaign I chose to send my squad to the MEC Bay and killed 2 chryssalids and a muton elite, and so missed the opportunity to ambush the flyers. I took up a strong defensive position in the Command Center, using smoke from my medic, and waited for the flyers to emerge from the Rear Guard Station. They trickled out, about 3 at a time. As expected, they targeted my blueshirts, and a cyberdisc killed one of them. The flyers usually manage to kill someone.

Before I could finish them off, more enemies had dropped into the MEC Bay (as usual this wave was mutons and berserkers) and I was once again frantically repositioning my squad, while still fighting in the Command Center. The Berserkers separated from their muton buddies and so I was able to fight them piecemeal, and then move into the MEC Bay where 2 of the mutons had gotten stuck at the bottom by the near wall, on overwatch, as they are prone to do. These were easy to dispatch, once I flashbanged them to remove the overwatch.

The 5th wave is only 3 enemies, usually chryssalids, and gives your squad time to set up a defensive position. There are 2 great places to play defense; along the rampart in the MEC Bay which has 2 elevated high cover positions, or at the back of the Command Center which also has 2 elevated high cover positions. In either area, it is possible to hide MECs behind walls, and peek out around corners with blueshirts to play spotter for squadsight soldiers. If you set up in the MEC Bay you can fall back to the Command Center should things turn ugly. If you set up in the Command Center, there is no where to fall back to, but the enemy may disperse more as they move into your position, allowing you to fight them on better terms.

The final 2 waves are certain to have at least one of the toughest enemies available. In March 2017, that means an ethereal or sectopod. They will also have other very tough enemies as well. In my most recent campaign the 6th wave was 2 drones, sectoid commander, cyberdisc, mechtoid. The 7th wave was sectoid commander, mechtoid, muton, ethereal.

Occasionally the aliens will go through the rooms on the left or right of the MEC Bay, and then pop out unexpectedly. You can position your blueshirts at the doors to these rooms, in order to anticipate it. The enemy came right down the center of the MEC Bay in my current campaign, and I was able to use battlescanners and blueshirts to locate them and shoot them from squadsight with my scout. The intel from battlescanners is really useful at this stage in the mission. When the ethereal reached the large gateway, I moved my MECs back a bit so that the ethereal would not get the first attack. This worked very well, and I was able to kill it before it could do anything. The other nasty enemies had bunched up with the ethereal, and so things got a bit dicey, but we pulled through. The only casualties on the mission were 3 dead blueshirts; we are eternally grateful for their bravery and sacrifice.

1. The 3 months do not need to be consecutive.

2. I am not certain that the 4 “No Drop Rounds” will occur exactly as I have listed them - but that is what happened in my last run.