[Psitticine]

I've been using tactical combat for situations like that. I don't really trust the strategic AI not to polish that enemy marble clean. It seems to even go for an undefended planet over mobile units like transports which have retreated to the corner of the map.

OTOH, when you do have a transport available, putting it in a fleet with Capture Planet orders works very well. Other ships, even ones in other fleets, will support the effort by going in and clearing out the WPs and other defenses before the transport(s) close.

I tend to put a few napalm bombs on my troop transports. They work *very* well against WPs, especially when you also carry enough point defense and/or shields and armour to make it through the initial wave of missiles.