After having my family sick for 5 days I eventually found some time to play a few hours and went back to Halo 3. Coming back after quite some time I started to try out some new moves and strategies. Then I came up with the idea to try to finish a mission without dying along the way. That said I wanted to start with a really hard mission and that was Crow's Nest. The problem with that mission is that it contains a least two battles that are really difficult. The first is initial battle in the hangar which has several waves of enemies and the ammunition is limited. The second is in the Motor pool where the is a horde of brutes including a brute chieftain with a deadly gravity hammer.
The battle in the Hangar is difficult because there are many hallways, corners and levels so that it is easy to get caught off guard or pined in a corner dying pretty fast. Trying to survive I figured out a nifty strategy that makes is nearly fool proof. First I enter the hanger through the right door, kill the grunts and make my way up to the upper level and move to the left immediately. From there I decimate the enemies using the battle riffle or the carbine. I focus on the brutes first and some of the close grunts. The rest is taken care of by the other marines. There it is also easy to evade the shots by the enemies and the Covenants phantoms. The only enemy that come up to this level is a grunt that comes from the right side. From time to time you might want to roam around to find find more ammunition like a needler or others. The last wave of brutes / grunts will stay on the floor of the hangar and so you can run around to find ammunition to take them out. When done go down to the hanger's floor and pick up a needler and fill it up. Then see if there is a turret around and if pick it up for later fights.
The next fight is in a cave right before the ops-center where a bunch of flying drones fight you. In the little room at the end of the hallway where you enter the cave there is a rack with battle rifles where you can get one and reload it. Because that crate fell over I could not hide behind and so I went back into the hallway taking the drones out. It turned out that the drones are not shooting at me if I am back in the hallway. There I could take out most of the drones without getting shot at. Then I picked up the turret again and made my way to the ops-center and to the hallway that leads to the motor pool. In this hallway I drop the turret, go back to the cave and pick up the turret on the right hand side and bring it back to the hallway.
Finally the battle in the motor pool is still difficult but I figured out some tricks to increase the chances to survive. First I open the door, drop the turret behind the shield and move forward to the ramp while switching to the needler. Either I throw a grenade or use the needler right away to take out one or two brutes. While being close I use the needler to take out the brutes. If I am in troubles I run back on jump through the hole in the orange metal wall and got behind the shield. Then I use the battle rifle to take out the brutes. First I focus on the golden brute with the brute shoot. Then I go to the left of the shield and take aim on the golden containers at the other end of the motor pool which will explode when shot at. This takes out some the right shield exposing the chieftain better. For some time there are no new brutes coming carrying carbines and I try to take out the chieftain with the battle rifle. Sometimes that works fine. If the brutes with the carbines appear or I run out of ammunition on my battle rifle I got right through the hole in the wall to the crate and fill up. As soon as the brutes with the carbine appear I retreat into the hallway to avoid their fire (high enough or into the left or right corner). From there I use the battle rifle to take them out one by one retreating back as soon as I am shot at but keep an eye on the chieftain or other brutes that may enter the hallway. If the chieftain comes to the hallway use grenades and battle rifle fire to keep him out and kill him there. If he enters run towards him and melee him several times until he is dead. It seems that he cannot swing the hammer while punched. When he is gone and everything seems quiet take a gravity lift (in front of the shield) and go up to the upper walkways. Be careful because a brute or two could still hide out. When all brutes are gone, reload the battle rifle, take the gravity hammer and the turret with the most ammunition. The turret helps greatly against the flying drone on the way to the barracks and to kill the brutes afterwards.
Have fun - Andy