diff --git a/Custom-campaigns.md b/Custom-campaigns.md
index 759022b..3f31615 100644
--- a/Custom-campaigns.md
+++ b/Custom-campaigns.md
@@ -122,6 +122,25 @@ iads_config:
 
 How the IADS Network works is described over here: [IADS Network](#iads---integrated-air-defence-system)
 
+### Overriding SAM positions
+
+It is possible to override the type of Air Defense unite that will be spawned by Retribution, provided it exists in the faction, otherwise standard generation behavior will occur.
+
+The syntax is as follows in the campaign file :
+```yaml
+ground_forces:
+  SAM-LR-BasselAlAssad : SA-5/S-200
+  SAM-LR-Palmyra : SA-5/S-200
+  SAM-LR-Aleppo : SA-10/S-300PS
+  SAM-LR-H3 : SA-5/S-200
+  SAM-LR-SouthLebanon: SA-5/S-200
+  SAM-MR-PalmyraLake: SA-6
+```
+
+The first part (for instance `SAM-LR-BasselAlAssad` in the example above) references the *group* name in the mission file.
+
+The second part (in this example `SA-5/S-200`) references the group name as present in the faction file or the definitions present in `resources/groups`.
+
 ### Common issues with a custom campaign yaml file and their solutions
 
 Below are solutions to common issues with a custom campaign yaml. Please also note that the yaml syntax is case sensitive: primary and Primary are considered separate keys, for example.