Saudia Arabia to buy S400 Trimuf long range Air Defense System........! Saudi Arabia has agreed to buy the Russian S-400 air defense system, a Saudi Television reported. The Dubai-based television channel also said that Saudi Arabia had signed a memorandum of understanding to help the kingdom in its efforts to develop its own military industries. And this is the second time in the last month that Moscow has sold its S-400 missile defense system to an ally of, and major purchaser of weapons from, the US. Last month, Turkey agreed to buy the S-400 defense system, which has further strained relations between Ankara and NATO. Salman arrived in Moscow on Wednesday, and it was the first time a Saudi king has ever visited Moscow.