Using Git Submodules

You will have to fetch submodules manually. Below a snippet of a wercker.yml step that does exactly that:

- script:
        name: install git
        code: |
            apt-get update
            apt-get install git -y
    - add-ssh-key:
        keyname: KEY_NAME
    - add-to-known_hosts:
        fingerprint: 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
    - script:
        name: initialize git submodules
        code: |
            git submodule update --init --recursive

Note: fingeprint values sometimes change, for the most recent information see: values for github and values for bitbucket