https://bugs.freedesktop.org/show_bug.cgi?id=102709
--- Comment #1 from Samuel Pitoiset samuel.pitoiset@gmail.com --- Well, War Thunder doesn't check that GL_EXT_texture_compression_s3tc is exposed before using those compressed formats.
Though, if you have libtxc_dxtn installed on your system the extension should be enabled, can you check?