According to the Stockholm International Peace Research Institute (SIPRI), 70 percent of Saudi's arsenal now comes from the United States. SIPRI tracks transfers of major weapons and is one of few organizations to do this.  

Saudi Arabia's appetite for weapons has grown as its regional ambitions have increased. The ongoing war in Yemen, and concern about Iranian influence, are both reflected in increases in weapons purchases by the Saudis over time.

"There's been a very significant growth in arms supplies to Saudi Arabia by the US," says SIPRI's Pieter Wezeman, a senior researcher and Middle East specialist. "To Saudi Arabia, the US supplies a very wide range of arms. The most important types of arms include combat aircraft, tanks and missiles. It includes very advanced sensors and intelligence gathering equipment, often on planes. In the coming years, it will also include frigates and other ships. So, really, the whole package of weapons which Saudi Arabia wants to have is what the US is willing to supply and already has supplied."