In a dramatic defence shift, the United Arab Emirates—one of Washington’s closest partners in the Gulf—is moving to buy Russian S‑400 air‑defence systems under a trilateral deal with Turkey and Russia. For Putin, it’s a win: Russian hardware gains a long‑term foothold inside a key Gulf ally. For Erdogan, it’s a way to offload a politically costly system and cash in diplomatically by regaining access to American stealth jets.