Action Reaction is a fairly open land map with many twists and turns that can promote diverse tactics.
The map is diagonally symmetric. Each player has a large starting area that includes three medium-sized ore patches: one rear, one middle, and one front. The rear ore patch is protected by a garrisonable factory structure and is near a civilian Construction Unit which can be used as a repair vehicle if stolen by an Engineer, Hijacker or Huntress. Moving clockwise: Just prior to the middle patch is a ramp leading to a raised area including an Oil Derrick, two garrisonable outhouses, and a bridge leading away from the home area. Further past the middle ore patch is a gem patch under the bridge, and further beyond that is an expansion area including an Expansion Post, Oil Derrick, Hospital, and another gem patch. The far edge of this expansion area contains a garrisonable lighthouse, an Artillery Bunker surrounded by water, and a SAM Bunker. These structures border a triangle of water forming the corner of the map which ultimately leads to a back entrance to the opponent's base area. All of the ore and gem patches have drills.
The neutral areas of the map are dominated by high ground. Each player can directly access their opponent's home area via large ramps leading to the square in the centre of the map, which is cornered by four Concrete Bunkers. From atop the map centre players can also take paths to the sides, where they will find the other end of their bridge, a down ramp to their expansion area, and the path to the opponent's back entrance (or vice versa). At the intersection of these three paths is a HMG Tower that can defend from or alert a player to flank attacks. The back path is also partially covered by another garrisonable building on the lower ground; however this will not protect against carefully managed attacks.
- Tech Oil Derrick x4
- Tech Concrete Bunker x4
- Tech Base Expansion Post x2
- Tech Hospital x2
- Tech SAM Bunker x2
- Tech Artillery Bunker x2
- Tech HMG Tower x2
Securing the gems on the home side of the map is absolutely crucial to success. Doing so is also an excuse to grab the two Oil Derricks and the Hospital on the way. This is perfectly achievable before placing the first Refinery as long as one knows where they're going. However, rushing the Expansion Post has to be weighed against the potential loss of map control and inability to deny enemy scouting. If the opponent manages to take control of the two raised Concrete Bunkers on the home side, the garrisoned infantry will be in range of the middle gem patch and far ore patch, denying those resources. Needless to say it will also make going up the ramp troublesome.
On a map such as this, it's also very important to consider flanking and sneak attacks. One path can be discouraged by taking the HMG Tower nearest the home expansion and/or building one or more turrets there. In any case one should be wary of a tank rush, as they can be difficult to defend from if caught off guard due to the distance between the main base and the Expansion Post. The two Bunker defences and the garrisonable lighthouse near the water are often neglected and if so will leave a means of getting into the enemy expansion with flying units or swimmers such as Crazy Ivans. A more obvious approach is the bridge leading from the home turf straight to the enemy back door.
Because of this, and because the opponent controls the other end of the water leading to the same path, and because one is already defending at least two locations already, it's very important to resist the urge to "protect" your important structures and instead creep forward. Putting important things at the back inevitably leads to someone running a Basilisk around the clockwise edge of the map and sniping them or something similar, and you probably won't be able to adequately defend all three routes simultaneously. Of course, that works both ways. Having uncontested control of the middle of the map allows one to strike in any possible direction and quickly pull an opponent to pieces.