BEST OBTAINED WITH A FRIEND!
Join a co-op ranked match together.
The biggest difficulty in obtaining this achievement is keeping your blue power bar high and never letting it start to go down. If the attacker picks all infantry, there will be JUST enough men on the field that if the defender kills each one PLUS the attacker’s hero TWICE, you will JUST make it to the Hero Vehicle.
So, at the start of the match, the attacker picks all infantry waves to attack. The defender builds ONE anti-infantry turret (I put mine in the large square in front of the box to have a straight view of anyone running into the box). Upgrade it fully (incidentally, you can customize the match to give you as much money as you need to start this way).
At the start, the attacker runs with their hero to the defending turret. The defender should take out the hero right before the other advancing attackers are in range. That way the bar will go up a bit at the beginning and then continue to rise as you take out infantry. As soon as the attacker’s hero spawns again (towards the end of the match), they must RUN to the defending turret. It is important that the defender shoot the SECOND Hero on the battlefield BEFORE they kill the last advancing infantry. Once the last infantry is killed, the round ends.
Both times I did this, the total number of infantry attackers (not missing one) and killing the Hero twice gave me JUST enough to get my vehicle call-in… After you reach the Hero Vehicle, getting the Barrage is cake! It will take less than half a round as your bar will not drop below the vehicle mark…
Once the barrage is available, call it in and pop goes the chievo!