diff --git a/.project/designs/app/src/data/units.ts b/.project/designs/app/src/data/units.ts
index 761471da..432456ed 100644
--- a/.project/designs/app/src/data/units.ts
+++ b/.project/designs/app/src/data/units.ts
@@ -1,6 +1,8 @@
 export type AttackType = "blade" | "pierce" | "crush" | "trample" | "siege";
 export type ArmorType  = "unarmored" | "light" | "medium" | "armored" | "heavy" | "plate" | "fortified";
 
+export type Domain = "land" | "air" | "sea";
+
 export interface Unit {
   id: string;
   name: string;
@@ -15,6 +17,7 @@ export interface Unit {
   range: number;
   movement: number;
   keywords: string[];
+  domain: Domain;
   race?: string;
   unique?: boolean;
 }