Starcraft AI blog

3 example games to give an idea how to cannon rush at the pro level, with lessons for bots in both offense and defense. This is only a taste of the range of variations—different timings and positions and mixes of techniques are possible.

a standard main-base cannon rush

This is the most recent pro cannon rush game: Jaehoon cannon rushed Shuttle in game 2 of their round-of-8 ASL match on 21 August 2016 (game 2 starts at 47:50 in the video). It’s an in-base cannon rush behind the main mineral line, and Jaehoon’s version is as standard as can be for a rare strategy. Call it a canon cannon rush. The requirements and steps were:

1. it works on 2-player maps, where you don’t have to scout the opponent’s location
2. there must be room to proxy where the opponent may not see
• here, behind the opponent’s main mineral line
3. send out one of your first probes: watch the north base in the minimap, a probe sets out immediately
4. sneak the probe into position: Jaehoon skirted the edge of the enemy base in hope of staying unseen
5. proxy a pylon, then a forge
6. build 2 rear cannons first, to fortify the position before it is scouted
• the rear cannons should be as sheltered as possible; Jaehoon used buildings and trees as shelter
7. around the time the 2 rear cannons finish, add 2 front cannons in range to attack
• the opponent will see the front cannons, but the rear cannons protect them

The opponent should know you’ve proxied as soon as they scout your base. They still have to find the proxy itself. If the opponent finds out in time to stop the 2 rear cannons from finishing, the cannon rush fails and the rusher is set far back.

In this case the cannon rush succeeded and Shuttle had to abandon mining in his main, but that was not enough in itself for Jaehoon to win. A pylon and 2 cannons already cost as much as a nexus, and the cannons can’t move. Shuttle canceled his gas and second gateway and built a nexus at his natural. Jaehoon was able to get gas and pull ahead in tech. Watch the rest of the game to see more followup!

These are the requirements and steps to cannon a pro. You see why it can’t be played often. It may be a little easier to cannon a bot!

Lesson for bots which cannon rush: Don’t go overboard. Jaehoon could have added more cannons and killed buildings, but the time and expense would have put him behind. Follow up with gateway units.

Lesson for bots which get proxied in any way: If the opponent’s base doesn’t have enough stuff in it, scout in and around your own base for a proxy. Ideally, count minerals and compare total mining to the buildings and units that you see. You may also want to scout the center of the map. If you want to be safe no matter what and don’t mind paying for it, don’t wait but always scout your own base (like some versions of Tscmoo).

Lesson for bots which get cannon rushed: If you can’t mine your main minerals, you still need to mine. Expand!

a Nal_rA natural cannon rush

In Nal_rA vs. Zergman from 2006 on Rush Hour 3 (a 3-player map), Nal_rA shows us a similar cannon rush, but executed later against the enemy natural instead of the enemy main. The requirements and steps:

1. there must be room near the opponent’s natural to proxy where the opponent may not see
• here, to the side of the opponent’s natural base location
2. this build works against an opponent who can be expected to fast expand—mostly zerg
3. scout at a normal timing
• I suspect Nal_rA decided on the build when his scout crossed paths with the overlord
4. build a pylon and forge in your main
• Nal_rA built the forge in the back where it might not be seen at first
5. sneak a second probe into position
• Nal_rA sent the probe in a loop to avoid any zerg scouts
6. build the pylon, 2 hidden rear cannons, and 2 front cannons as above
• start the front cannons as the hatchery finishes
• zerg benefits if the hatchery can be canceled in time

Zergman reacted in an interesting way, and the game is entertaining.

Lesson for bots that get cannon rushed: Zergman’s sunken colonies remind us that sunkens can keep cannons away. Zerg bots need to learn how to place sunkens to keep the cannons from pushing ever closer. Protoss bots can place counter-cannons for the same purpose. Terran... has more work to do until tanks come out. Terran should build away from the cannons and be prepared to float buildings to new spots.

a Nal_rA cannon containment

Not as standard as first two example games. In Nal_rA vs. Orion from 2007 on Blue Storm, Nal_rA shows us how to build up a cannon containment even against strategically correct counterplay, by also proxying gateways. Orion opened 9 pool, the best opening if you get cheesed, and still ends up crushed by Nal_rA’s strong creative play. The requirements and steps:

1. it works on 2-player maps, where you don’t have to scout the opponent’s location
2. send out a very early probe
3. predict the overlord scouting path to avoid being seen
4. build a pylon, then a forge
5. Nal_rA made only one cannon before the first gateway
• variations are possible
• this variant emphasizes adding zealots in early
6. add more cannons and zealots until the containment is tight
7. after or while doing that, defeat any forces outside the containment
8. if the last step is successful, then the enemy is weakened and the game is almost over

Look at the beautiful placement of that first cannon, walled in by terrain, minerals, geyser, and the pylon and forge. That is what makes the build work; without that excellent placement, Nal_rA would have to build 2 cannons before the first gateway and would have fallen behind in mobile units. Even the next cannons are tucked behind gateways to reduce their attackable surface. Nal_rA did not build cannons in the open until there was enough defense to protect them as they warped in. At some point I will look into the wall-building code in LetaBot and see whether it can be adapted to uses like this.

Zerg opened with the safest anti-cheese opening, 9 pool, and followed up in a strategically logical way at every point. Orion did make tactical mistakes, though. The good moves:

1. send zerglings across the map to force Nal_rA to warp cannons in his main
2. get an expansion, so as not to be trapped on one base
3. switch to hydralisks, which are more efficient against zealots and cannons

Zerg could have countered the proxy by scouting his natural: Hold the first overlord there for a while, or send an early drone to check it. When the proxy is found, pull drones to stop it, and zerg is ahead. But if protoss were playing normally, then the extra scouting effort would put zerg on the back foot.

Lesson for bots which get cannon contained: It’s important to have a worker outside the containment. Keep your scout alive, or send out a worker before the cannons finish. Cannons mean that your opponent has little offensive force yet, so you can fast expand at any convenient base. Produce forces at your new expansion and you can go for the enemy main, or sandwich the containment, or whatever you want. Other reactions may be good too depending on the situation, but this way is natural, and I’ve never seen a bot do it.

Update: Cannon like a newbie basher. This 3 minute video shows a cannon rush in which you block off a space behind the enemy minerals with 2 pylons and place a cannon between them, where it can’t be reached. You’ll never see this rush in a pro game, because it’s trivial to beat if you know how to push units through the minerals. But I have never seen a bot that knows how to push through the minerals.... This variant has the advantage of simplicity; it works on many maps and in a wide variety of situations.