How do you get “Ain't No Cavalry Comin” achievement?

Question

The steam description for Ain't No Cavalry Comin' says "Have a soldier survive every mission in a full game".

Two questions regarding this:

In the first mission with the tutorial on, only one guy survives. Does that mean he is the only person that I can use to unlock this achievement?

If a soldier gets injured and gets placed in the medbay and cannot go on a mission, would that mean he couldn't be used to get the achievement?

Answer 1

One Soldier needs to be in every mission, so he is not allowed to be injured, or only very little.

What you could do is go for increased squad size early and make sure this particular soldier is always in your team and gets never injured. I cannot imagine doing this in ironman, but on easy and with loadable savegames this should be quite possible, since the achievement does not state any difficulty.

Also avoid the tutorial, since you can beat the first mission without losing anyone then.

Answer 2

I just finished my playthrough for this achievement, so here are my observations:

• Easy difficulty is the way to go. Ironman should be disabled, just in case. This is going to take several hours, and there's no point in losing it at hour 9 because you left this box checked.
• Disable the tutorial for sure, as this gives you a chance to bring home everybody from the first mission. I don't know if the first mission is counted, but I went ahead and picked one of the four from that mission anyhow.
• Since avoiding injury is the name of the game, pick someone who will hang back. I used a sniper with squad sight - I'd almost recommend starting over from the beginning again if none of your initial four turn out to be sniper class.
• Give this person heavy armor + any health bonus items you have access to. Titan Armor + Chitin Plating = less chance of medbay time.
• I gave them a nickname like "Required" or "Achievement" so I knew right away if they were in the squad. If you've got the Elite Soldier Pack, you might also consider coloring them differently.
• Psi training is pretty much out - it takes 10 days, and I've found it extremely rare that I go 10 days without a mission.

The early game was the trickiest part - at the beginning I actually had 3 soldiers who had been in every mission, just in case. However, once I had squadsight and a plasma sniper rifle there wasn't much left to do but win.

I played the game to delay the assault on the alien base until I had done almost all the research I possibly could. The enemies are pretty easy prior to the mind controlling aliens showing up, so this reduced my risk of injury or death. This took a bit of panic management with satellite coverage, but this is Easy difficulty, so it was nothing major.

Once I assaulted the base, I pretty much beelined the story missions and required buildings in order to get to the end as soon as possible.

I didn't have to skip any missions - my sniper never ended up in the medbay, and everything went fairly smoothly on the whole. The achievement popped for me when I was at the closing statistics screen.