The Defense Units are objects that appear in Shadow the Hedgehog. They are devices which are part of the emergency defense system around the Space Colony ARK, designed to create a defensive barrier around the Colony to block any outside invasion.
The Defense Units are large, floating and green crystalline devices, with large diamonds-shaped parts connected to each other in the shape of a six-pointed star. Each is protected by large glass plates and have GUN Cruisers for protection.
In The ARK and Space Gadget, the player's dark mission is to destroy the Defense Units in order to let the Black Arms take over Space Colony ARK. To achieve this, the player must destroy them using firearms, though they will be protected by glass barriers that can block a limited number of the player's attacks. They also have GUN Cruisers that attack intruders. The player has to destroy six Defense Units in Space Gadget, and four in The ARK.