Starcraft AI blog

One of the themes of today’s SSCAIT broadcast by Nepeta is that too much static defense is bad for you. He repeatedly showed in ZvZ that the side which made too many sunkens tended to fall behind. Static defense can’t go attack; it costs resources and it offers initiative to the opponent. In a well-played game, static defense has to pay for itself with a countervailing advantage: You have to use the temporary safety it brings to get ahead in economy, as in a protoss forge-expand opening or as Killerbot by Marian Devecka tries to do, or to get ahead in tech, as when in ZvZ you make a sunken to tide yourself over until your spire finishes.

But there is a reason that so many bots play turtle strategies. Turtling is strong against bots which do not adapt, which is most of them. For Steamhammer, I added 1 base and 2 base turtle openings which crush Wuli, an opponent that Steamhammer otherwise struggles against. Wuli does not adapt.

Steamhammer does adapt to static defense and pulls ahead of opponents that turtle too much. When the opponent makes static defense, you have 3 broad strategic choices. They are the same 3 choices you always have, but the opponent has offered you initiative so any of them might give you an advantage. 1. You can pull ahead in army and bust the defenses. Example: Hydralisk bust versus protoss forge expand. It can win outright, but it is risky. 2. Use the opponent’s passivity to pull ahead in tech. If you made a sunken, other things being equal I can safely skip a few lings and get a faster spire. 3. Or similarly, pull ahead in economy. If you made sunkens, I can make drones.

Steamhammer primarily adapts by making drones. A protoss or terran bot might expand sooner instead, so it can build workers faster. But whatever the choice, you want to adapt so that you don’t end up crushed like Wuli.

The game Steamhammer vs KillAll (correcting the unfortunate typo in the bot’s name) is an example. KillAll opened 9 pool with extractor trick to get 10 drones, and Steamhammer unluckily chose 5 pool. It is a build order win for KillAll—if both sides play well, the 9 pool wins with little risk.

But instead of making a second hatchery to win with mass lings, or getting quick gas to win with mutalisks, KillAll turtled. It threw away its advantage.

You may want 1 sunken, because the 5 pooler starts making lings sooner and can be a little ahead. 5 sunkens are 4 too many and put KillAll behind despite its stronger opening. They are not well placed; they don’t protect either the approaches or the mineral line.

If I had been playing, I would have made a moderate number of drones, teched fast, expanded once for a second gas to guarantee that I would stay ahead, and aimed to win with mutalisks. Steamhammer made many drones and teched slowly (fast enough not to fall behind), spending the extra income on zerglings. It went up to 5 hatcheries to produce a biblical flood of zerglings. The picture shows 3 of the 5 hatcheries; the other 2 are in the natural. Steamhammer is slightly ahead in economy and tech and way ahead in army and production capacity. Steamhammer can only lose if it blunders.

The zerglings were so many that they cracked the turtle shell and overran KillAll. GG. KillAll lost drones right off because the sunkens were misplaced, but it took only a fraction of the zerglings to finish off the sunkens. Steamhammer had a completed spire but did not need any mutalisks (see how many purple zerglings are already en route).

Steamhammer’s reaction to static defense is effective. You can beat it with a turtle strategy, but only by exploiting weaknesses. The reaction to static defense is not a weakness.