This issue is caused by corrupted game client files.
To solve the issue, please, try the following:
1. Check files integrity in the launcher of the game:
If you are using Steam version, you can verify the integrity of game files via properties:
2. Delete local settings folders. By default, they can be found here:
- C:\Program files (x86)\War Thunder\Cache
and for Steam version:
- C:\Program Files (x86)\Steam\steamapps\common\War Thunder\Cache