Doomsday machines

Destroying a homeworld by star demolition requires two catastrophes, and the defender will try to prevent each of them. The most obvious way to circumvent any possible defense is to create each overpopulation all in one turn. The all-at-once technique is achieved with the traditional Doomsday machine.

Traditional two-turn Doomsday machines are difficult to make. In particular, you must be able to sacrifice two large yellows ships. There are only three large yellow pieces in the game, and if two of them are controlled by the enemy (either as ships or stars), a traditional Doomsday machine may be impossible.

However, there are Doomsday machines with lower material requirements. They simply require extra turns to operate. Doomsday machines usually destroy the two stars in two separate "phases:" bring in ships to destroy one star, then bring in ships to destroy the second star.

Each phase can take 1-3 turns to complete. If each phase can be completed in one turn, then it's a traditional Doomsday machine.

Your opponent may not notice your Doomsday machine as it gets constructed, but even beginners sit up and take notice if you move a ship to their homeworld, let alone if you destroy a star. They will go on high alert, look for your plan, and search for a way to stop it. You must expect your opponent to mount all possible resistance to your lethal threat. The next two sections discuss multi-turn Doomsday phases and how your opponent can attempt defenses in the middle of a phase.

Even if you have all of the pieces ready, there is a one-turn pause between the phases of a Doomsday machine. The echoing boom of the first star's supernova dies down, it's your opponent's turn, and they know that it's time to do or die. Expect your them to quickly attack your home or the components of the other half of your Doomsday machine. See this section for a discussion of your opponent's resistance between phases.

Destroying a star in two turns

Destroying a star in three turns

• The second ship poses a threat of victory by direct assault, i.e., your opponent will not survive if the ship gets a chance to perform captures. Usually this means that your second ship is large and you have a large red somewhere else that could be sacrificed to capture their entire home fleet.
• The second ship can build its way to overpopulation, i.e., there are at least two bank pieces of that color and you have a medium green that you could sacrifice. Under those circumstances, your opponent must capture your second ship (or block the build) to prevent you from building two more matching ships and destroying the star by building rather than by moving in the third piece ship.

1. You move one star-colored ship to your opponent's home.
2. Your opponent captures your invading ship.
3. You move another star-colored ship to their home.
4. Your opponent makes a choice:
   • They capture the second invader
     • In this case, you can simply move a third star-colored ship to their home and trigger the catastrophe.
   • They try to avoid overpopulation by to reducing the concentration of that color. Their choices are to sacrifice, move, or trade the first captured invader.
     • This is why your second ship needs a backup plan. You either build to make a catastrophe or capture a lethal amount of the opponent's defense.
5. You move another star-colored ship to their home.

On steps 2 or 4, your opponent may decide to do something else entirely. Unless you are going to win on your very next turn, your opponent may find that defending is useless and look for other opportunities. The two-turn star demolition gives your opponent one free turn, but the three-turn demolition gives them two. These free turns are in addition to the turn that your opponent will get between your Doomsday phases. Study the position very carefully looking for surprise desperation sacrifices before you engage a three-turn Doomsday phase.

A word of caution about red: This section discusses in detail the fact that, if the star is red, sacrificing the red ship that they just captured from you and attacking your large ship can be done in one move, which defends against both the star demolition and direct assault threats. In other words, three turns is too slow to demolish a red star.

In the image below, Beta has assembled a Doomsday machine with two three-turn phases. In the notation I use in the glossary, this is a 3g/3y Doomsday machine. Notice that it would not work as a 3y/3g machine (overpopulating yellow first then green) since the yellow ships are needed for the greens to advance.

Beta safely destroys both homestars of Alpha via

In the particular scenario above, Alpha must capture on moves 2 and 5 because otherwise Beta may win by direct assault by sacrificing r3 or achieve the catastrophes by sacrificing g3. In many scenarios, the defender may simply ignore the small invading ships and use the turn productively.

No slow red catastrophe

Your opponent can't usually cause a red catastrophe against you by moving red ships one at a time. If they attempt this, here's what should happen

1. They move a red ship into your system.
2. You capture the first red ship.
3. They move another red ship into your system.
4. You sacrifice the first red ship to capture the second red ship.
5. They see the error of their ways.

For example, in the position below, Beta has just blundered by moving r3 into Alpha's home. Alpha should sacrifice the r1 and capture the invader. Beta has regrets.

You should check your own situation carefully, however. You must have a ship large enough to capture any invading reds, and—if you are defending a red system marker— you shouldn't let your only large ship be a red one. If your only large ship is red as well as a system marker, then you won't be able to sacrifice the r3 to capture an invading r3, so a slow red catastrophe can happen when your opponent moves in with their second red ship.

Basic direct assaults

Of the three paths to victory, the direct assault seems to get the least attention. Every strategy guide talks about Doomsday machines (the surest way to achieve star demolition) and the Bluebird mistake (allowing a game-losing fleet catastrophe). New players may not have a clear idea of how a direct assault occurs, so their first exposure is likely to be a defeat they didn't see coming.

Typically, every player has a large ship in their homeworld and a red ship someplace (which they could sacrifice). If your opponent doesn't have a red ship, they'll probably at least have a planetary defense system. So if you move any ship into your opponent's home, they'll just capture it, right?

Not if you invade with several ships at once so that they can't all be captured. Your opponent's defenses will determine the size of the invasion fleet you need. I need to define some variables to keep the next section from being too wordy.

• The number of large ships that your opponent has in their home is L.
• Your opponent's largest red ship is of size R.
  • If they have no red ships but a red homestar, it counts as a small red ship, R=1.
  • If they have no access to red, R=0.
  • If they have a large red in their home and that is their only large ship in their home, then ignore that ship when finding R because that R3 can't be sacrificed for capturing large invaders.

Here's what you need for what I call the "basic" direct assault:

• R+1 large ships poised to move into your opponent's home. These are the "invaders."
• A yellow ship of size R+1 (not one of the invaders).
• A red ship of size R+L (not one of the invaders).

Here's the battle plan:

1. You sacrifice your yellow ship and move your R+1 large ships into your opponent's home
2. They sacrifice their largest red to capture R of your invading larges (you still have one left)
3. You sacrifice your red ship to capture the R ships that they just captured as well as the L large ships that they had to begin with.

You now have two or more large ships in your opponent's home and they have none. Usually, their only defense at this point (besides a counterattack) is to catastrophe your larges.

If R+L is more than 3, then a basic direct assault won't work. You could theoretically have a two-wave invasion with more than three ships, but that's more complicated than I'm going to illustrate here.

Compared to catastrophe-based wins, direct assaults can be difficult to plan. When you're invading and capturing ships, you need your ships to stay alive (unlike when you're pushing ships into catastrophes). Your opponent has time to fight back, so it can get confusing. You need to examine your own case carefully to figure out how to invade.

Examples

Beta wins with a basic direct assault.

• Alpha's maximum red power is R=1.
• Alpha has L=1 large ship at home.
• Beta can move R+1=2 large ships to Alpha's home at once.
• Alpha is expected to capture R=1 of the invaders.
• Beta can then capture all R+L=2 larges in Alpha's home.

Beta wins with a basic direct assault.

• Alpha's maximum red power is R=2 (not R=3 since their R3 is the only large ship in their home and can't be sacrificed for captures).
• Alpha has L=1 large ship at home.
• Beta can move R+1=3 large ships to Alpha's home at once.
• Alpha is expected to capture R=2 of the invaders.
• Beta can then capture all R+L=3 larges in Alpha's home.

Beta wins with a basic direct assault.

A basic direct assault cannot work because

• Alpha has R=3 red power and
• Beta cannot possibly bring R+1=4 ships to Alpha's home in one shot.

So if Beta invades with three, the invaders are simply captured.

However, if Beta moves just two ships to Alpha's home, Alpha is forced to sacrifice their only red ship, which reduces Alpha's red power to R=0. Yellow can then launch a second stage with R+1=1 large ship and win.

Beta has enough material for a basic direct assault, but the invasion still fails because the invading ships are both blue and Alpha can defend with a catastrophe.

A basic direct assault would fail because

• Alpha has L=2 large ships and R=1 red power and
• Beta does not have a red ship of size L+R=3.

However, Beta can still conduct a successful invasion by capturing Alpha's only red ship (instead of following the basic direct assault formula by capturing a large ship).

Importantly, Alpha did not have any way to get more red once the invasion started. If Alpha could have built a red ship in their home after Beta invaded, then Alpha would still have a red ship after Beta captured one. Then Alpha could capture it back, and the position would repeat endlessly, ending the game in a draw.

Plan for complete, swift victory

Destroying one of your opponent's stars usually costs you at least three ships. A two turn demolition can be achieved with three small star-colored ships and a y2--if you're lucky enough to have all three small ships of the star's color. Otherwise, you'll be destroying two or more of your own mediums and/or at least one large (more on what ship size combinations can be used to destroy stars here). In many games, that much ship destruction is enough to turn the balance of material power in your opponent's favor.

2. Your opponent's homeworld gained connections

After a star's destruction, your opponent's home is connected to systems with stars of the destroyed star's size (the hyperspace bypass principle). If that star was a size that is in your own home, your homes are now connected (assuming that the universe was originally large). Having connected homes may give your opponent a chance to counterattack.

3. The bank is refreshed

The bank now has the pieces involved in your catastrophe, the stars of any systems that you abandoned, and your sacrificed ship (if you used one). Your opponent may be able to trade or build the pieces that you just returned. If you were barely containing your opponent's advances before, then the new ships might be just what they need to get back in the game. This is especially true if your move returned a y3 piece to the bank. A new y3 ship might give your opponent the mobility they need to give you trouble.

...so minimize the come-back risk

Destroying a homestar can throw a game into chaos in the ways listed above, and you should minimize the length of the chaotic period by destroying the second star as quickly as possible. If your plan to demolish the second star requires you to build more ships or to move ships to different systems, try to perform these preparation moves before destroying the first star.