Okay since 2 commenters seem to have trouble getting the mod.

@dukery @desertfox151

1.
please check if there is a turtle tank.zip file in your mods directory.
the usual path of the directory is
C:\Program Files (x86)\Steam\SteamApps\common\Xenonauts\assets\mods
2.
IF YES extract the zip archive file right in this very same folder, and the mod should become visible.
3.
IF NOT you can download the zip file from my google drive from this URL:
https://drive.google.com/file/d/1btNgzYkgmC77tHJ_mR8HCtnwbhnCy_sJ/view?usp=sharing

4.
after download you need to copy it into your folder stated under 1. you can either extract the zip file by hand there yourself or let the mod launcher do it.