Base Defense (TFTD)
Purpose
Most of the information on Base Defence is found on the link at the bottom of this page. This page is to discuss any differences in Base Defence missions that are specific to TFTD.
General Discussion
For TFTD Base Defence missions, there is mention in some articles that the spawn points are different, that aliens will routinely appear in places other than the Airlock and Sub Pens (not just if the aliens run out of their own spawn points).
From personal experience (one Base Defence so far!), the spawn points do appear to be different, it looks like perhaps some of the aliens can spawn in adjacent modules to the usual spawn points, while most of them spawn in the usual modules. Or did I read somewhere that they start in the normal modules but get 1-2 turns free movement? I don't think so, as I had 2-3 aliens who were nearly the whole way on the right hand side of the base, when the access lift "channel" on the extreme left side of the base. So I think they teleport/leak through into adjacent modules to the sub pens and access lifts.
Still, the overwhelming majority of aliens were in the normal spawn points - sub pens and access lift - so a few leaking behind the lines does not invalidate the overall Base Defence strategy.
Some more points about TFTD Base Defence missions: underwater-only weapons (HJ Cannon, Torp launchers, etc) are automatically excluded from your 80 item limit, so you don't need to sell/transfer them. This was a help for me because a battleship hit me with no warning (near end of February on Superhuman). I did not get anything on sonar (long range and short range). Possibly it was because I had time advance set to 1 Hr, but you would still expect to get a popup box and for the clock to stop when the incoming battleship is detected. No such luck for me.
To Do
Discussion of how the module tiles are different (if at all) in TFTD - which ones have clear killing zones, which ones have tricky little hidey holes, etc.
See Also
The main article on Base Defense, though it is focused on UFO: Enemy Unknown (XCom 1).