[Freeciv-Dev] (PR#10694) AI Builds Doomed Ferries and Passengers

["Benedict Adamson" <badamson@xxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=10694 >

Consider a player who wants to attack overseas. She should build land 
attack units and enough ferries to carry them to their targets. However, 
the land units will be vulnerable to enemy warships while being ferried. 
She should therefore consider building naval escorts first, or favour 
ferry routes through safer waters, if her enemies have naval 
superiority. If she does not, she will waste resources used to build the 
attackers and the ferries.

The current AI is not so wise. When deciding whether to build an attack 
unit, it takes into account (in function process_attacker_want) the 
distance to the target (the function uses military_amortize with 
move_time) and the cost of building a ferry (the needferry variable). 
But it does not take into account the danger of being sunk.

This AI weakness is particularly noticeable when an AI player has been 
forced back to their home island and they have a strong enemy (or 
alliance of enemies) who has a good navy around the island but is not 
yet strong enough to invade the island. The AI player will repeatedly 
build ferries, load artillery on to them, sail them one turn out of 
port, and let them be sunk by waiting destroyers and cruisers.

Note that the current faulty enthusiasm the AI has for building ferries 
(PR#10216, see http://rt.freeciv.org/Ticket/Display.html?id=10216 ) 
masks this problem: the AI's enemies can't sink the vast fleet of 
transports fast enough.