On this page of our guide to BioShock Infinite you will find the second part of a detailed walkthrough of Chapter 39 - Command Deck. In our walkthrough, we suggest how to destroy Vox airships that can lead to the arrival of hostile reinforcements.
The appearance of the Vox airships will occur some time after the start of the final battle in Chapter 39.
The Vox airships are capable of dropping more reinforcements aboard the main Comstock airship where the final battle of the game takes place. Destroying these zeppelins should become your top priority and it's best to use the Songbird for this. Don't forget about the troops stationed on the deck of your zeppelin, because you still have to prevent the generator from being destroyed. Once you destroy the last airship, the main battle will end after a moment.