I was playing around today and found a way to re-use my transports mulitple times.
I fleeted 3 transports and assulated a fairly low morale planet with INFO warfare to get a few more troops.
The assualt went so well, I had a few extra troops left over then my initial invasion force. These troops went back to the transport leaving only the left overs from the info warfare. (100-200 left on the planet.) The transport fleet was still there with movement left over to go to the next planet.
I tried this a couple of more times and found out that any full transport from the transport fleet would survive. My transports were 1500 troop capacity. If I assualted with 4500 troops off 3 transports and 3232 troops survived then 2 transports would survive and 232 would remain on the planet.
The questions is: Is this an intended use for transports , that only the number of transports needed for the invasion to be successful are expended and the rest survive?
Using Info warfare seems to currently allow all to survive if enough people are converted to the attackers side. Perhaps 1 transport should always be expended out of the fleet.
I have not be able to duplicate this with a single transport only with a fleet of transports.
Earlier related discussion here
https://forums.galciv2.com/?ForumID=346&AID=106385#830437