Players select their race (Iron Marine, Nemoidian, Atlantean, or Elect) and unit type and are then launched into battle.

Each of the four races features four unique, upgradeable unit types ranging in ability from the fast and agile to the large and powerful.

Undertow is set underwater, where an aquatic alien race known as the Elect launches an attack on the polar ice caps, causing them to melt and flood the planet.

With the city of Atlantis thawed by the melting of the ice caps the Atlanteans also become a threat, vowing to reclaim the planet and rule again.

On April 23, 2007, Chair Entertainment announced through a company press release that Undertow was in development for Xbox Live Arcade.