diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 000000000..728c1bbfd
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,13 @@
+[submodule "ext/tug"]
+	path = ext/tug
+	url = ../tug.git
+
+[submodule "ext/iphreeqc"]
+	path = ext/iphreeqc
+	url = ../iphreeqc.git
+[submodule "ext/ai-benchmarks-utils"]
+	path = ext/ai-benchmarks-utils
+	url = git@git.gfz-potsdam.de:naaice/ai-benchmarks-utils.git
+[submodule "ext/ai-surrogate-poet"]
+	path = ext/ai-surrogate-poet
+	url = git@git.gfz-potsdam.de:naaice/ai-surrogate-poet.git
diff --git a/ext/ai-surrogate-poet b/ext/ai-surrogate-poet
new file mode 160000
index 000000000..1a2dfc6a4
--- /dev/null
+++ b/ext/ai-surrogate-poet
@@ -0,0 +1 @@
+Subproject commit 1a2dfc6a48fb82b86d142c297db539315d135797