diff --git a/scripts/acme/migrate_dir_to_cime b/scripts/acme/migrate_dir_to_cime
new file mode 100755
index 000000000000..9980a6d654b1
--- /dev/null
+++ b/scripts/acme/migrate_dir_to_cime
@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+
+import sys, os, os.path
+from acme_util import expect, warning, verbose_print, run_cmd
+
+cwd = os.getcwd()
+
+if __name__ == '__main__':
+    if len(sys.argv) != 5:
+        print('usage: migrate_dir_to_cime ACME_ROOT acme_subdir CIME_ROOT cime_subdir')
+        exit(0)
+
+    acme_root = os.path.abspath(sys.argv[1])
+    acme_subdir = sys.argv[2]
+    cime_root = os.path.abspath(sys.argv[3])
+    cime_subdir = sys.argv[4]
+
+    # Check dirs.
+    if not os.path.exists(acme_root):
+        print('Invalid ACME root: %s'%acme_root)
+        exit(1)
+    if not os.path.exists(os.path.join(acme_root, acme_subdir)):
+        print('Invalid ACME subdir: %s'%acme_subdir)
+        exit(1)
+    if not os.path.exists(cime_root):
+        print('Invalid CIME root: %s'%cime_root)
+        exit(1)
+
+    # Do a subtree split of the ACME subdirectory.
+    os.chdir(acme_root)
+    run_cmd('git checkout master')
+    acme_subdir_branch = 'acme/%s'%acme_subdir
+    print('Creating ACME branch %s for subdirectory %s...'%(acme_subdir_branch, acme_subdir))
+    run_cmd('git branch -D %s'%acme_subdir_branch, ok_to_fail=True)
+    run_cmd('git subtree split --prefix=%s master -b %s'%(acme_subdir, acme_subdir_branch))
+
+    # Set up a remote for this ACME branch for CIME.
+    print('Setting up %s remote within CIME repo...'%acme_subdir_branch)
+    os.chdir(cime_root)
+    run_cmd('git checkout master')
+    run_cmd('git remote remove %s'%acme_subdir_branch, ok_to_fail=True)
+    run_cmd('git remote add -t %s %s %s'%(acme_subdir_branch, acme_subdir_branch, acme_root))
+
+    # Now fetch it.
+    print('Fetching %s...'%acme_subdir_branch)
+    run_cmd('git fetch %s'%acme_subdir_branch)
+
+    os.chdir(cwd)
+
+    # Now give our poor little user a hint of how to proceed.
+    print('Now you can merge the ACME subdirectory into CIME using:')
+    print('cd %s'%cime_root)
+    print('git merge --squash -s recursive -Xsubtree=%s remotes/%s/%s'%(cime_subdir, acme_subdir_branch, acme_subdir_branch))
+    print('And resolve conflicts with:')
+    print('git mergetool')