A Brief Introduction
Yes, I am aware there are similar threads on this in the forums. I think this offers a bit more practical advice though, instead of complex tactics taken out of military handbooks that don't really apply to NS very well.
Strength in numbers is a common mantra in NS, but numbers are not the only factor in a squad’s effectiveness. Often, large squads of marines are demolished by only a few skulks because they function poorly as a group. Here, I am going to go through some things that can be done to allow a squad of marines to perform to their maximum potential.
Consider the above figure – the orange triangle is an alien, and the blue circles are marines. The problem should be immediately apparently to any experienced player – the marine in the front is in the line of fire of the two marines behind him. At best, the two marines are useless because they cannot damage the alien in their current position, and at worse, they are a liability with friendly fire on.
In this figure, we see the marines abreast of each other. Now the marines have overlapping arcs of fire – by simple rearrangement, we have increased the effective firepower of the group against the alien threefold. Damage from a single LMG is unlikely to kill a fade before it can retreat. Three LMGs are a dire threat to a fade if he decides to loiter around.
And yet, this formation still suffers from potential problems. By just rotating our simple line, this group of marines is still vulnerable from attacks from another direction. Even worse, because they are spaced so closely, the marine on the left cannot jump backwards to put some distance between himself and the alien. Once the alien on the left kills the first marine, he has only a short distance to cover before entering attack range of the next marine.
Now we see a sort of a triangular formation. Not only do the marines have room to dodge, they can cover each other’s backs. Although optimal positioning will vary depending on the situation, the basic rules to keep in mind is to allow all members room to maneuver and maintain clear lines of fire.
Unfortunately for marines, NS maps rarely consist solely of long, straight hallways. One thing I’ve often observed is marine teams splitting up as they move. One common scenario pictured below:
Because the marine in the front is too fast for his teammates (Or his teammates are too slow), he has to fight an alien without any fire support because the corner is in their line of sight. This could easily be avoided by just having the marine in the front not move down the hallway too much, as shown.
As the alien approaches the marine, he will place himself within the firing arc of his teammates. Of course, an even better solution would be to have marines move as a group so that the first marine does not need to wait for his teammates.
Lastly, in an ambush situation, marines should be covering whatever entrance for aliens they are closest to and have a line of sight to. If your squad is under attack and you are in the back of the team, it is your responsibility to cover the group’s rear, not pump a clip of LMG into your teammate’s back while trying to hit a skulk that will most likely be easily handled without your help. If your squad lacks enough marines to cover all possibly directions of an alien attack, then you will need to alternate your attention between different entrances. Resist the urge to reload immediately after an alien dies, unless you are critically low on ammo – the fraction of second it takes to switch weapons/cancel a reload often means the difference between killing a subsequent alien and dying.
Please feel free to repost this on other forums - in fact, in the interest of better gameplay, I encourage you to do it.
Edit: I'll probably do a write-up on basic alien tactics some other time.