To begin this mission liberate the Insula Dracon settlements, pick up a chopper and head north to Massos. Speak with Dimah then follow the pipes until you reach the enemy base. Take out the base to remove the FOW threat from the area, then head to the next destination marker and continue to follow the pipes through the tunnel.
Take out the soldiers and boats in the lower area, then swim through the small tunnel to find the underground site. Go through the tunnel under the base and continue to swim to the next destination marker. Make quick work of the enemies that attack, then destroy the nearby transformers and head out of the cave to complete the mission.