The Kirov Airship is the Soviet's main bomber air unit. These units are extremely slow and cumbersome but if they get over a target, it is as good as dead. The damage this unit deals to every type of unit on the ground is huge and is an extremely effective base killer. You should always protect your Kirovs with air superiority fighters like the MiG so your Kirovs are not destroyed before they get to your opponent's base.
The Kirov Airship's secondary ability is Hydrogen burn. This allows the Kirov to move faster towards a target, but you also have to make a health sacrifice. The longer you use the increased speed, the more your Kirov will be weakened and much easier for the enemy to kill. Unless you are close to your enemy base the Kirov will take more damage than the speed increase is worth.