With the lightning rods doing their job, return to the Emperor’s Tomb and inspect the Right Hand of God. You may notice here that there are three protrusions on its sides that look suspiciously like battery terminals.
When you leave the bunker again, a Nazi airship arrives and starts launching rockets at your position, forcing you to stay mobile or indoors. Occasionally, blast doors open on the ship’s underbelly, revealing giant glowing weak points.
Return fire against the blimp using the best long-range weapons at your disposal (i.e., light machine guns or rifles). Cause enough damage to the weak spots and the blimp loses one of its battery packs, which crashes to the ground in the village. Ideally, try to score the final hit on the blimp when it’s above the village square or the courtyard near the Catacombs, as those are easy places to defend.
When you get a battery pack on the ground, set up a perimeter around it and power it up by killing nearby zombies. It’s finished charging when the majority of it blows up, leaving behind a more portable battery. Carry the remains to the Emperor’s Tomb and install it in the Left Hand of God.
You must wait a couple of minutes after every successful battery run for the blimp to return. Once it does, however, knock another battery off it and repeat the process. It takes three batteries to power the Left Hand of God, which lets you move on to the next stage.