The Underground Add-on for Tom Clancy's The Division has 5 achievements worth 150 gamerscore.
Access the Tactical Operations Center.
Complete each of the 6 different mission objectives in the underground.
Reach Underground Rank 40.
In a group of 4 finish an Operation on Challenge with 5 directives enabled.
Retrieve all 55 Audio Logs and 25 UrbEx Diaries the Underground.