Map: Lost Platoon
The idea behind Firefight is fairly simple... DON'T DIE. That is why I will repeat some strategies that others have mentioned but will emphasize some some key differences.
Our Result: I ended the match once the achievement was reached, 1 hour and 57 minuets, 31 lives remaining (even with many intentional betrayals). One of our players had never beaten a single level in any halo on heroic and prefers easy mode. The strategy only requires one truly great player and one who is exceptional. The other 2 just need to know how to aim, fire, and communicate.
Lost Platoon is a map that revolves around a central structure. It is connected to the only 2 ODST spawn points by an upstairs walkway. The key point of interest will be your main base located in the side of the central structure. It is the Warthogs spawn point, and the room on the side of it contains the Spartan Laser. Enemies can only enter the map via Phantom dropship, there are 4 potential locations. 2 phantoms will land at the beginning of each sub-round. 2 of the locations are Chopper drop points and 2 are Wraith drop points. The most important being the wraith drop point directly visible from the Spartan Laser spawn room. The other wraith will stay up on the hill on the opposite side of the map.
SPECIFIC TEAM ROLES AND STRATEGY
Role 1: Laser
Probably the key player, but also your weak link skill wise. Let me break it down simply.
1. Hide in Laser spawn room with Laser.
2. Kill the visible Wraith immediately upon drop.
3. Hide. Don't Die.
4. Repeat when needed.
This simply and, quite honesty bor-ring, job is what makes the systematic rape of these Covenants possible. The only reasons this player can EVER die is through a breakdown of team support combined with restlessness. Literal death by boredom. He will poke his head out at just the wrong moment, and this will be to the delight of a Brute Chieftain carrying a Fuel Rod or Hammer. Spartan Laser will be abundant if used for these purposes. So much so that this player spent the second half of set 4 killing us! (the easiest set) Also note that the Wraith on the back hill is nearly irrelevant, and no player should climb that hill for any reason. Most of the time he is off in his own world not even firing, but even when he was firing it resulted in 3 deaths tops. I'd take that over risking the lasers safety every other sub-round any day.
Role 2: Brute Chopper/Leader
Reserve this role for the best player of your group, but be warned you will likely die the most. Not only will they be expected to thrive in any combat situation, many times with no support!!! but you will need to be able to communicate important details to your teammates. Mostly this will include dropship locations as well as what enemies have, or are going to, drop (for that you will need to understand the pattern of sub-rounds that the enemies are based upon). It is also important to understand skulls and let your team know because you may wish to adjust your strategy (EX. when Catch is active the safest place for all team members is in a chopper, except the laser). As for the physical expectations of this player, you should be out killing in a Chopper at all times. When necessary (and your chopper is destroyed) you may need to take out any group of opponents on your own, on foot, then get back to base asap. For that I recommend your weapons to be a Plasma Pistol and either a Carbine or Human Pistol, whichever has more prevalent ammo at the time.
1. Splatter any large enemies, as well as shoot Drones.
2. Never approach a dropsite when a phantom is present.
3. Always travel clockwise around the central structure and be cautious of collision with teammates in other choppers. Doing this will avoid ALOT of senseless deaths and provides you with the best angle of approach for all dropsites.
3. At the time of a drop focus on killing the enemies closest to the base first, that way you will ensure the protection of your Laser (and possibly other players) within it.
4. The Leader especially needs to be adept at killing the driver of enemy choppers without destroying the vehicle. Storage of spares should be inside the base under the stairs, and a player should get in and out of them from time to time to prevent them from disappearing. SIDE NOTE - Another solution suggested storing the choppers in the 2 spawning rooms. While it is an interesting idea, after some thought I would disagree with it's practical effectiveness. Spares aren't always plentiful and finding where you put them then getting to them would be more trouble then it saves you. It's easy enough to run up the stairs and follow the path to the choppers in the base without ever needing to engage an enemy.
Role 3: Chopper When Possible
This player should be fairly skilled. Basically follow all chopper rules as stated above. When you can't use a chopper then stay in the base and support your teammates.
Role 4: Alternative
If this player is skilled enough then use a chopper when you can like Role 3. However there is a very effective alternative if this player isn't that good or like in our case prefers the simplicity for time to time (this is also what you should be doing if no chopper is available at the time.) Sit in the gun of the warthog and DO NOT move it out of the base. In the base you're are protected on all sides except the one you should be shooting towards. This strategy should be avoided when Catch is active or during a sub-round that contains Hunters or Brute Chieftains wielding Hammers or Fuel Rods. Also this is the main difference between this solution and others.... NEVER.... NEVER use the Warthog as an offensive weapon outside the base. First of all that means 2 deaths, and second its tactically foolish. Death risk if far too high. Trust me, stick with choppers, boosting makes splattering any enemy possible without driving directly at them from a distance to gain speed (seems obvious). It would be incredibly daft to try this when any fuel rod or hunter is around.... which is often (let alone almost any enemy). Plus if you think you can rely on the turret, think again, the Tilt Skull will make it nearly impossible. On top of that the Warthog isn't safe. Go with choppers, that wheel is an offensive and defensive advantage. If you get stuck on the wheel if barely even affects you.
BONUS ROUND TACTICS
Everyone go for headshots with a pistol or carbine and avoid getting stuck. The medals will drastically increase your points in a short amount of time. Once the target score is reached try to run and survive the 60 seconds so you don't risk losing your weapons or grenades. Also there is no sense wasting a chopper and getting simultaneously stuck 10 times. But it is possible to do good damage with the chopper during the round, just be wary.
Catch - Stay on the move and use choppers
Tilt - (Ground Tactics) Take out enemy shields with plasma weapons, use headshots. (If you use the chopper tactics then Tilt won't affect you at all.)
Black Eye - Use extreme caution!!! When there is a lone grunt or jackal the chopper players should dismount and beat down to replenish stamina. Oh and 2 healths are located on the back wall of the base and 2 are on the walls on top of the bases structure. Even so, the majority of your deaths will occur when Black Eye is active.
If you follow these stratigies this achievement will be almost easy. In my opinion it was an actual "walk in the park" compared to the rigors of the highway and the Vidmaster Deja Vu Achievement (yes that was a bit of a pun). I would say good luck but you won't need it. Have fun slaughtering these Covenant.