Starcraft AI blog

A ferry drop is when you use the same transport (or transports) repeatedly to bring more units over. If it’s across a single cliff, you can also call it an elevator. A ferry drop is usually over a short distance, of course.

See the video of Oriol defeating Krasi0 in 2010 (!) by constantly ferrying units on Python from 6 main to 9 main. Oriol is a zerg player and went off-race with protoss this game. The bot lost because it kept units at the front of its natural instead of defending its main with enough forces. I’m sure Krasi0 today would put up a tougher fight, but bots still don’t try to interpret their opponent’s intentions so they are easy to take off guard.

Bots that invest heavily in static defense at their natural are likely to be vulnerable to early ferry drops into their main. XIMP is the obvious example. Also Killerbot seems vulnerable in ZvT before its lurkers are out, and in ZvP before its mutas are out. Where ferry drop works in the early game, other early flying tricks like zerg slow drop and terran factory float are also likely to work.

A ferry drop is more likely to succeed if you can keep it unscouted, whether by distraction or by force or by knowing where your opponent can’t see. Of course those are advanced skills.

Ferry drops are especially menacing if you can ferry a dangerous army into the enemy main before it is noticed. I could be wrong, but my guess is that the stratagem is more likely to succeed against zerg bots. Protoss and terran have spread-out buildings which give vision over more terrain in their bases. Zerg should have no trouble monitoring its borders with overlords, but most bots don’t.