The Atlas AS7-D is one of the most famous and feared 'Mechs of all time. Its Autocannon 20 alone is capable of crippling lighter 'Mechs in one shot. Adding to that the quartet of Medium Lasers and SRM 6, the AS7-D is a dangerous short to medium range combatant. The LRM 20 adds long range bombardment capability.
The AS7-D-DC is a modification of the AS7-D that equips the newly reintroduced Command Console. This piece of equipment enhances the MechWarrior's command and control capability. To make room for this, Two Medium Lasers and a ton of ammo are removed. Also notable, is this Mechs ability to carry an ECM.
The AS7-K is a new production model of the Atlas that sees the return of several Lostech technologies. Tonnage is freed up through the use of a light weight XL Engine. Almost the entire weapons loadout is replaced with one designed for long range fire. Most notable is the Gauss Rifle. While doing slightly less damage than the traditional Autocannon 20, the far superior range more than makes up for it and compliments the range profile of the LRM 20. Additionally, two new ER Large Lasers adds reliable long range punch while two Medium Pulse Lasers add accurate close range punch. Finally, for defense, the AS7-K includes an Anti-Missile System.
The AS7-RS is a Succession Wars era version of the Atlas that attempts to recreate the Star League's Atlas II using technology available at the time. The result is a 'Mech with a focus on medium ranged combat in contrast to the AS7-D's close range brawling loadout.