Game:

Valkyria Chronicles (2008)

Duration: 8:33

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6

In which the best Anti-Tank Sniper of our Sniper Elite class takes potshots at a radiator her way. Also in which I consider this a full clear because when the operation was complete, there were no enemies on the field.
Technically, a total of eight more units show up as reinforcements after the Federation's Turn 3 ends. But as they are reinforcements that are spawned using the "Reinforcements have appeared" method (like when they spawn from an enemy camp), none of them are leader units or Aces or the like. And so I don't believe they count in performing a full clear if the stage is completed before they arrive.
I'm fairly certain Marina is the only Sniper Elite capable of taking out the APC by the end of Turn 2 -- Cezary's Backup Sniping only seems to give a buff of +25%vsArmor among other boosts, while Marina's My Way personal potential gives, among other boosts, +50%vsArmor!
As is shown by Knute taking a potshot at the APC's radiator, Anti-Tank Snipers are going to be the only way to damage the APC in any feasible way if the vsArmor-boosting orders aren't used.
Worth noting is that the Sniper Elite method is probably better than the Trooper Elite/All Units Damage method as Snipers continue to be very useful for both missions in Chapter 10, and the large boost in AP and Accuracy gained by becoming Elites is worth its weight in gold given the amount of time save that would otherwise be spent trying to recover from a missed Sniper shot. (After Chapter 10, enough EXP is amassed to have all classes up to Elite status.)

For a clear of this stage using Trooper Elites and the All Units Damage order, see this link:
https://www.youtube.com/watch?v=D-RGJv4QLdY

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