aaahhh, the commando. everyone remembers the first time they ever held a SCAR. or at least, i remember it. anyway moving on.
Commandos are technically the squad leaders. This is because they can see invisible enemies (including the patriarch) that are within range, and see enemy health bars when specimens get within range.
The primary role of the Commando is to take out the weaker specimens; these being the Crawlers, Clots, and Stalkers. While all Perks are effective at taking out weak specimens, the Commando has a very large stockpile of ammunition for assault rifles, and when i say large, i mean like 10 or 12 clips full for the SCAR. Although, the Bullpup lacks the firepower of the weaponry geared towards Support specialists and Sharpshooters. It is one of the best weapons in the game for landing critical headshots. Even so, Commandos now have a tier 2 weapon in their arsenal, namely the AK47. These properties make the Commando the ideal squad member to take out the fast/stealthy specimens that might interfere with the other squad members while they focus on the more dangerous ones such as the Fleshpound and the chainsaw-wielding Scrake. Commandos should communicate with their team when the stealth Patriarch is invisible to hunt him down and prevent him from healing. unless you want the game against the patriarch to end with him laughing at your feeble attempts to kill him. Commandos in the squad should focus on protecting the people in the front lines from the silent, deadly Stalker and Crawler that love to sneak up on squad members and blind them or simply block their path. Stalkers have the nasty habit of causing one's screen to go red when attacked, which temporarily blinds the Player and can cause them to run into a deadly situation. Crawlers are fast moving, travel in packs or swarms, and have a weak but quick leap attack. The Commando should be on the lookout for these specimens at all times to protect their squad-mates.
The Commando is probably one of the hardest specialities to level due to the requirements for their next level.
Kill X Stalkers
Killing stalkers is probably the one side of the requirements for the commando that can be done easily. The only thing is that stalkers aren't all that easy to see until the later levels and if you miss one then another team mate who meets them up close will kill them instead. Thus meaning that it's going to be difficult for you to kill a large number of them quickly.
Deal x damage with assault rifles
This one is the hard side of the commando, although the weapons you can use to achieve this are in a large number the only thing is that these weapons don't deal a lot of damage and thus really getting the damage count up is going to be a long process so expect to play Commando for a long time in the later levels before you can get to the final 2 levels.
The commando is really the back-bone of the team and VERY useful in the right hands.