In order to resolve this issue, please follow the instrictions from this article:

• TCP/IP stack reset

If this doesn't help, please perform a clean boot:

1.  Press the Windows(Win) button and R key at the same time. The Run dialog box will open. Type MSCONFIG and click OK. This should open the System Configuration Utility window.
2. Click on the Services tab and check the Hide All Microsoft Services checkbox near the bottom. Do not continue unless the box is checked. Click Disable All.
3. Go to the Startup tab and click Disable All.
4. Click OK and restart your computer.
5. Do not start any other programs and try the game again.

 Also, make sure that all necessary ports are open in your system:

• "War Thunder" game ports