From the preiviev of Hades operation:
As stated above, only soldier units can enter the metro and the sewers. Additionally, these units must enter the battlefield by the end of the second round of the game or risk being left behind. It is akin to suicide to get stranded in the underground, and any unit in an underground scenario that has not been deployed by the end of the second round is considered to be eliminated.
OK, so how in god's name can i not move my units into the BF in the first round? There is such an option even?