In Update 0.8.7 Wargaming changed the AA mechanics in the game. One of these changes made it so that only ships with long-range AA capabilities can make use of aerial explosions. Because of this, the “AA Guns Modification 1” upgrade has become ineffective on certain ships that don’t have a long-range AA defense zone.
Therefore, players will be compensated in the amount of 250 000 credits for each ship in their port which both does not have a long-range AA zone, and has the “AA Guns Modification 1” upgrade installed.
Compensation credited by: Tue. 03 Sep. 23:59 CEST (UTC+2).
I personally hope that they will change this mechanic because some ships without a long-range anti-air already struggled before against carriers but now, they don’t even have flak bursts to have a bit of hope that the enemy planes would lose a big portion of their HP.