Caution: This achievement is missable
I personally used the XCOM Wiki for information whilst trying to pop the achievement myself, so I give my thanks to its writers. If you wanna check out the page in question it's http://xcom.wikia.com/wiki/Medals
The achievement requires that the one soldier you nominate as 'the Volunteer' (which is a plot-required event, see the spoiler at the end for more details if you wish) has one of each Medal, for a total of 5 Medals rewarded to that soldier. This achievement is not at all hard; it's just very easily missable. When you are rewarded new Medals, just save one of each until you can create the Volunteer.
I can confirm that you can re-obtain Medals from dead soldiers. Just meet the Medal requirements and you may be rewarded with his/her prior Medals. Unfortunately, simply dismissing a soldier to get his Medals does not seem to work
-- he/she must be killed. I'm not sure if the game ignoring the dismissal is a bug or not (I'll update this if I'm ever aware of something for it in a patch).
The above method to re-reward a Medal to a different soldier will work for all Medals except for the 'Star of Terra'. This can only ever be obtained once
. This makes the achievement missable
(because the person with this exclusive Medal may die / be dismissed / might be ignored on a covert extraction mission / or may not be eligible to become the Volunteer).
The Medals are;Urban Combat Badge
Awarded for: Completing an urban map mission
+5 Defense while in cover.
+5 Aim against enemies in full cover.I went for the +5 Defense bonus, as, with Rapid Fire for my Assaults, and SCOPEs for my Snipers+Heavies, as well as other Aim bonuses, I feel Defense was what I really lacked. Plus, my soldiers are mostly always in cover, meaning the bonus is more active than the other; which applies when the enemies are only in -full- cover.Defender's Medal
Awarded for: A soldier dying or being stabilized during a mission. may also awarded for killing a seeker before it starts to strangle a soldier.
- Never panic as a result of allies getting wounded or killed.
- Medikits and Restorative Mist heal 2 HP more when used on the soldier.I rarely experience Panic (I play Enemy Unknown/Within on Easy and Normal) so with that I simply chose the +2 healing factor, though you might want the former if you chose higher difficulty.International Service Cross
Awarded for: Complete a mission outside your base's continent (your starting location).
+2 Will per different nationality in the squad.
+2 Aim per continent that XCOM has earned.My squad, as may yours, may differ based on who is injured or who's been eligible for the Gift. And there was only one member of my squad who had the Gift, so, other than Panic which I rarely suffered, Will wasn't much a factor for me. And thanks to my paranoia in not losing any countries, I was able to make use of the Aim bonus to its maximum.Council Medal of Honor
Awarded for: Completing a Council Mission
+10 Aim and Critical Chance if not within 7 tiles of an allied unit.
+1 Aim and +1 Will for each mission without any soldier deaths (to a maximum of +10 each).I usually group my squad together except when I anticipate enemies, so that I may flank them. But when I'm flanking them, I tend to have the advantage anyway, so the first bonus seems diminished to me. Whereas the second bonus for Aim and Will is constant as long as no one has died recently -- and I just reload my save when someone has. So with that, I took the second bonus.Star of Terra
Awarded for: Completing the XCOM Base Defense mission
Entire squad receives +5 Will and +5 Defense in battle. Robotic units only receive the defensive bonus.
All soldiers in the squad at Lieutenant rank or lower receive +25% XP for completing missions.I chose the first one as this was a no-brainer for me; most of my preferred soldiers were already quite well-levelled, and the bonus XP has limited effectiveness, unless you purposely swap out your squad members for weaker ones. The first bonus, for Will and Defense, seems much better and effective to me.
Gameplay spoilers (regarding how to create 'the Volunteer'):
"And remember Commander, we will be watching." :)