diff --git a/src/effectvehicle_base.h b/src/effectvehicle_base.h
--- a/src/effectvehicle_base.h
+++ b/src/effectvehicle_base.h
@@ -23,8 +23,8 @@
  *  - bubbles (industry)
  */
 struct EffectVehicle : public SpecializedVehicle<EffectVehicle, VEH_EFFECT> {
-	uint16 animation_state;
-	byte animation_substate;
+	uint16 animation_state;  ///< State primarily used to change the graphics/behaviour.
+	byte animation_substate; ///< Sub state to time the change of the graphics/behaviour.
 
 	/** We don't want GCC to zero our struct! It already is zeroed and has an index! */
 	EffectVehicle() : SpecializedVehicleBase() {}
@@ -35,6 +35,10 @@ struct EffectVehicle : public Specialize
 	bool Tick();
 };
 
+/**
+ * Iterate over disaster vehicles.
+ * @param var The variable used to iterate over.
+ */
 #define FOR_ALL_EFFECTVEHICLES(var) FOR_ALL_VEHICLES_OF_TYPE(EffectVehicle, var)
 
 #endif /* EFFECTVEHICLE_BASE_H */