Core and Support

Your Force is divided into Core and Support Choices.  For the Martian Colonists, the Core of a Platoon-level Force always consists of one Officer, his Command Squad and 2-3 Squads.

Your Support Choices represent other units attached to or temporarily supporting your Lieutenant and his Platoon.  Your Support choices vary depending on whether you are the Attacker or the Defender in the scenario you're playing.  Attacking Forces have more aggressive and mobile choices; Defending forces get more guns and fortifications.  In addition, Attacking Forces get 150% of the points a Defending Force gets, to compensate for the difficulty of making an assault.

(In case you're wondering, two Forces meeting each other in a symmetrical scenario both count as attacking, and have equal point levels.)

Platoon Level Support (Attacker)
0-1 Artillery choices with the following limits:
    0-1 Artillery Squad
    0-1 Motorized Artillery Squad
    0-1 Mortar Squads
0-2 Armor choices with the following limits:
    0-1 Armored Car Squads
    0-2 Light Tanks
    0-2 Light Infantry Tanks
    0-1 Medium Tank
    0-1 Heavy Tank
    0-1 Tank-Hunter
0-1 Gun choices with the following limits:
    0-1 Anti-Tank Gun Squads
    0-1 Heavy Machine-gun Squads
0-2 Troops choices with the following limits:
    0+ Infantry Squads
    0+ Cavalry Squads

WW1 German tank. Wikipedia.

Platoon Level Support (Defender)
0-1 Artillery choices with the following limits:
    0-1 Artillery Squad
    0-1 Motorized Artillery Squad
    0-1 Mortar Squads
0-1 Armor choices with the following limits:
    0-1 Armored Car Squads
    0-1 Light Tanks
    0-1 Light Infantry Tanks
    0-1 Medium Tank
    0-1 Heavy Tank
    0-1 Tank-Hunter
0-2 Gun choices with the following limits:
    0-1 Anti-Tank Gun Squads
    0-1 Machine-gun Squads
0-1 Troops choices with the following limits:
    0-1 Infantry Squads
    0-1 Cavalry Squads
    Fortifications (Platoon Level)

German bunkers of Longues-sur-Mer battery in Normandy, France. Wikipedia.