Halo 4

IDarK VorteXX's solution is spot on. This achievement can be a little bit tricky as it's tough to keep yourself in good shape whilst making sure all 6 friendlies are not being smashed to bits too!

I've put together a video which will hopefully give those struggling a bit of help with this section of the mission. This video is recorded on Heroic difficulty - Solo starting from the beginning of the mission.

Please note: You CAN start from Rally Point Bravo and still unlock this achievement if you've played and completed the mission once already. (Thanks to https://www.trueachievements.com/gameman9.htm for the confirmation on this)

This is done on mission 4 'Infinity' on Heroic.

SPOILERS

When you meet up with Lasky, he will tell you to clear an LZ. After that you will have 2 marines with you. When the door opens up go throught it and you will be greeted with a fight against 4 or more crawlers and a knight.Take out the crawlers with the DMR's that are near the sandbags and then forcus on the knight. An easy way to get rid of the crawlers is to headshot them resulting in an instant kill.
After this in the same area another knight and a watcher will spawn. Take out the watcher first then go all out on the knight.
Make sure that the two marines are alive when all the enemey in this area are dead.If you fail just revert to the checkpoint.

After this,you will have to go up a dirt hill and will be greeted once again with 5 crawlers and a knight in a narrow passage. Take out the crawlers then the knight.

As you go around the narrow passage you will see 4 more marines making it a total of 6. This area is the final area and is the hardest. Take out the crawlers first then the knight. Once again if you fail revert to checkpoint.
Once the enemies are dead, walk forward and one watcher will appear on each side above some rocks. They will spawn turrets if you dont kill them quick enough. If this happens revert to checkpoint. Once they are gone focus on the crawlers and try to draw as much fire from them as possible so the marines wont die.
The only help i can give you is to destroy the watchers before they build the turrets and draw as much fire from the crawlers as possible. An easy way to get rid of the crawlers is to headshot them resulting in an instant kill
Once the crawlers and the 2 knights are dead and you have 6 marines wait for a checkpoint.

The objective now is to press the button near the giant door and defend the hill you're on. A lot of crawlers will appear with knights , just try your best to kill them all. Once they are dead count your marines before a checkpoint.
NOTE: There is one marine all the way at the back on a turret on the left side of the hill. Make sure there are 6 marines. This achievement will take a lot of skill and a lot of reverting. It will be easier if you do it in co-op as there will be 4 of you.


From comments ive looked at it looks like the AR is effective against the knights shields. I never used an AR so thanks for that tip.
Also, once the marines have survived the onslaught up the hill, they will get on turrets and help you defend the hill. As always try to move forwatrd and tank all the damage so the marines wont die.

The achievement will pop once you press the button near the door again.

Hope this helps

If your going to vote negative please tell me why so i can improve this guide.

I did this on Solo Heroic, which was fairly difficult, but is doable. There are two groups of marines that you need to keep alive: the first 2, and then gain four more. Make sure to utilize revert to last save!

Hello everyone, This is another achievement guide for Halo - We are trying to make this as easy for you to follow as possible - As we do with all of our guides.

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This is one of the hardest campaign achievements you will come across in Halo 4. This takes place on the 4th mission and will require you to keep 6 marines alive. This has to be done on heroic difficultly(or harder), and can also be done in co-op. This guide was done in a solo play-through. Couple tips I can give you, always give the marines better equipment don't leave them with just a handgun. Also always take point and try to take all the damage and kill all of the enemies quickly as possible. Last always keep an eye on how many marines you have if any die or become missing restart the checkpoint before you proceed.

Tips:
- 6 marines must survive (you start with two and come across four more a bit later);
- always check if they are alive;
- if one of them dies, restart checkpoint;
- play on Heroic difficulty;
- you should have at least one coop partner - it is very hard to do alone;
- rush from the start and try to kill enemies as soon as possible;
- when you meet second group, eliminate all enemies and then move forward.

I got this achievement on coup with 2 other players (special thanks to cr1msonmoon & Bigdanzo51169). We played on Heroic.

Important to know:

- Always try to stay infront of the soldiers and try to take as many hits, so they can survive.

- When you arrive at the spot where the 4 soldiers are, then you need to play slowly. Don't rush it, first beware the line and kill what you see. If you start running straight to top, you will have to many enemies that spawn, what will lead to dead soldiers. When you killed all the first enemies, start advancing an again, stay infront of the soldiers and kill all new enemies. If you are fast enough you can even destroy the flying enemies so they can'y make those laser canons.

- When you are on top count howmuch soldiers you have left. We had 6 soldiers, but i'm not sure if you realy need 6 to get the achievement. Make sure that you have enough ammo so you can step in to the final part.

- Once you have insert Cortana, you will have multiple enemies spawn. Just stay infront of the soldiers, and kill everything, it's not so hard. One cortana says she's done, a few crawlers will come, kill them and go pick up cortana, and then you will get your deserved Clos to the Bros achievement.

I made a video of the things I just wrote so enjoy.

ps: this is my first solution, so any suggestions and constructive criticsime are greatly appreciated. And also tumbs up if you like my solution ;)

Here is my guide from my channel, Toslow Gaming. Easier said than done. Load up Rally Point Bravo on Mission 4: Infinity. There will be six Marines total. When you start out, two Marines will be there. As you progress, you meet up with four. After a whole survival scene on a hill, Cortona will want you to pick her up. Do so, and the achievement should pop up.Regularly, do a body count of the six Marines. Make sure you put HD.

I got this just the other day and I just want to add a few extra points to the GREAT solutions already available:

1) It's not as hard as I thought it would be! It's certainly not easy, and I did have to reload checkpoint at least a few times, but it's actually a really short chunk of mission that they have to be kept alive for (because you only have to load from Rally Point Bravo, as others have mentioned), so I got it completed in only 10-20 minutes.

2) Always run ahead. It's better that you die being too ferocious than a marine dies from you hanging back and have the enemies target one of them.

3) When you get to the bit where you have to defend Cortana, let the marines on the turrets (rather than hopping on one yourself). They are ABSURDLY good on them.

4) If you see a dead marine body on the floor it doesn't necessarily mean you've failed - there are a few bodies that are 'scripted' and will always be there. I reloaded once or twice as soon as I saw them, and then thought to actually count how many marines I had left and I still had the right number. Go off how many are left alive, rather than if there's a dead body or not! As others have mentioned, there should be 6 alive at the end of the fight. For me, there were 6 alive plus 1 dead body, and the achievement still popped, so the dead body was definitely already there. Hopefully this will save someone else a few unnecessary reloads!

Hope that's helpful. Give it a go on Solo before you try and get a party together - you might be surprised!