diff --git a/repo.py b/repo.py
index 0b26657..d5eb18d 100644
--- a/repo.py
+++ b/repo.py
@@ -98,6 +98,15 @@ def git_update(self):
 
             shutil.copy(f"git.{self.name}.out", self.suite.full_web_dir)
 
+        if self.suite.updateGitSubmodules == 1:
+            # update submodules to those specified by the current commit
+            # (--init is required because there may be new submodules since the last checkout)
+            self.suite.log.log(f"git submodule update in {self.dir}")
+            _, _, rc = test_util.run(f"git submodule update --init")
+
+            if rc != 0:
+                self.suite.log.fail("ERROR: git submodule update was unsuccessful")
+        
     def save_head(self):
         """Save the current head of the repo"""
 
diff --git a/suite.py b/suite.py
index 5a5bd81..bebe5cf 100644
--- a/suite.py
+++ b/suite.py
@@ -419,7 +419,7 @@ def __init__(self, args):
         self.useCmake = 0
         self.isSuperbuild = 0
         self.use_ctools = 1
-
+        
         self.reportCoverage = args.with_coverage
 
         # set automatically
@@ -435,6 +435,8 @@ def __init__(self, args):
         self.amrex_install_dir = "" # Cmake installation dir
         self.amrex_cmake_opts = ""
 
+        self.updateGitSubmodules = 0
+        
         self.MPIcommand = ""
         self.MPIhost = ""
 
diff --git a/test_util.py b/test_util.py
index d0ba0ab..0da1da8 100644
--- a/test_util.py
+++ b/test_util.py
@@ -28,6 +28,9 @@
   isSuperbuild   = < 0: pre-build AMReX and source (default)
                      1: CMake downloads AMReX and needs separate configure & build >
 
+  updateGitSubmodules = < 0: don't update submodules when changing git branches (default)
+                       1: run `git submodule update --init` after changing git branches >
+
   sourceTree = < C_Src or AMReX >
 
   suiteName = < descriptive name (i.e. Castro) >