Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

git submodule init
git submodule add git@github.com:dclong/docker_image_builder.git
git submodule update --recursive --remote

To remove a Git submodule.

git rm submodule

Module Already Exists in Index.

in file .gitmodules - delete links to submodule (whole section with submodule name)

in file .git\config - delete links to submodule, as in previous step

in folder .git\modules - delete folder with relative path similar to relative path of "problem" module

References

https://www.vogella.com/tutorials/GitSubmodules/article.html

https://stackoverflow.com/questions/12218420/add-a-submodule-which-cant-be-removed-from-the-index/39189599