Type means something like "Scout" or "Strike Cruiser".
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During the creation of the BoP mod, I've spent some time testing how the AI would react to certain changes in the ship lineup. I'll post the results here, maybe some of you may find it useful
- The AI cannot decide to build a certain ship class, it can only decide to build a certain ship type. It will then build the first ship of this type in the shiplist that's available (i.e. the one with the lowest ID).
- The AI will build more ships if the ships are cheaper. On the other hand, maintenance costs seem to be neglected, and I'm not sure if the AI even has to pay the full maintenance.
- Some ship types must be available to the AI player before it can build certain other ship types. The AI player might still occasionally build a ship of a type whose "prerequisite type" is not available.
A scout must be available so that destroyers can be built.
A scout and a destroyer must be available so that cruisers can be built.
A scout, a destroyer and a cruiser must be available so that strike cruisers or battleships can be built.
For example, if an AI player only has access to a scout type ship and a cruiser type ship, then it will exclusively build the scout.
EDIT:
For in-depth information see here:
viewtopic.php?f=9&t=707