Attack

Attack, represented by the icon is the amount of damage a unit adds to the damage a player can inflict on the opponent's units each turn.

The two most common ways units add their attack values to per-turn damage are:
 * Automatically at the start of the turn. In this case, the unit provides constant damage.
 * By using its ability, triggered by clicking on the unit. Usually, these units are blockers when not using their ability, so this trades defense for damage.

Value of Attack
The Tarsier attacks after 1 extra setup turn, and the cost for 1 faster Attack is about 2, while Gauss Cannon and Steelsplitter get it less efficiently from costed resources.

Thus a player could consider the Efficiency as similar, but early on, the fast Attack unit gets little value, as the defender gets to use the starting Defense as Prompt, as well as extra from the Absorber.

Delaying the Absorb once can be efficient as well, such as paying 5B late 1 turn and getting 2 Drones first, losing less than 2 from the Engineer lost. The loss of paying for Attack as delayed Attack makes a lone Gauss Cannon a value of 4G this way, as the opponent gets 2 Drones and a Blastforge after taking the hit. Extreme case:

(High Econ DDDC / DDDDC)
 * 1) DDDEG / Drones + Animus
 * 2) DDDDG / Drones + Blastforge + Tarsiers
 * 3) DDDDGA / Doomed Wall...