Age of Empires Series Wiki

Allows your Explorer to quickly train a small ambush party of Blowgun Warriors.
—In-game description

Carib Ambush Party is a technology in Age of Empires III that can be researched at a Trading Post built on a Carib settlement once the Commerce Age is reached. Once researched, it allows hero units to train up to 12 Carib Ambushers, which are statistically identical to Carib Blowgunners but are trained twice as fast.

Note that Asian civilizations who can have two Monks at the same time cannot train more than 12 Carib units. They can, however, train units simultaneously to reach a total of 12 Caribs between the Monks.