I've got a setup with several expanding AIs (which are brutal early in the game) and have tried several times to quickly build a Seabee and surround a city with mines... except that one of the expanding AI's transports just sails right through and takes the city. I've tried with two rows of mines... same result, multiple times in different games - and the message report shows absolutely nothing except that the enemy transport took the city. HuH? If I drive one of *my* cruisers into a mine I see a battle report... so the question is: Are transports immune to mines? If so, a note in the manual is probably warranted.
PS: This is on v5.0.17 under Ubuntu Linux 16.04LTS