I had to manipulate submodules quite recently and I faced issues where the HEAD of my submodule was not pointing where it should.
According the man page, a git checkout does not update the HEAD of a submodule.
So let's say the parent is on commit A, the submodule HEAD is on B but after the checkout it should be on C.

How can I check on which sha1 it should be ? Where is it stored in the .git ?