Mere hours after the Americans deployed the THAAD in Israel, the Pentagon announced a $1 billion payment from Saudi Arabia toward its acquisition, reflecting both countries' concerns about Iran’s continued missile program.The American Terminal High Altitude Area Defense (THAAD) system arrived in Israel on Tuesday along with some 200 troops from US European Command (EUCOM) for a month-long drill between the two allies. According to the IDF, the purpose of the tactical deployment of the THAAD is to “practice rapid deployment across the globe of complex systems, and to enhance cooperation with the IAF’s Air Defense Systems,” adding that “the IDF is working in cooperation with US forces to enhance coordination between the two militaries and to strengthen the ability to defend Israeli airspace.”Israel’s air defenses currently include the Iron Dome, designed to shoot down short-range rockets, the Arrow system, which intercepts ballistic missiles outside of the Earth’s atmosphere, and the David’s Sling missile defense system, designed to intercept tactical ballistic missiles, medium- to long-range rockets, as well as cruise missiles fired at ranges between 40 to 300 km. Washington and Israel have signed an agreement which would see the US come to assist Israel with missile defense in times of war and, according Uzi Rubin, the former head of the Arrow anti-ballistic missile project, this drill should not be looked at as one taking place due to regional events but as one which should have occurred years ago.According to Rubin, the Americans deployed the THAAD’s Army Navy/Transportable Radar Surveillance (AN/TPY2) radar to Israel as far back at 2012 with American troops operating it. The mobile AN/TPY-2 is a high-resolution X-band radar array which is designed to search, acquire, track, and differentiate inbound threats. It provides additional early warning against ballistic missile launches from close to 3,000 miles away.“The question is why wasn't it brought in before because the entire deployment of the Israeli systems is that all systems should be interoperable. This requirement was from the start, from the 1990s, that all Israeli systems would be designed to speak with American systems,” Rubin said. A spokesperson for EUCOM told The Jerusalem Post that a “deployment of this nature requires significant planning time. However, the purpose of a rapid deployment is that the unit doesn’t know the order is coming and they must react quickly, usually in a matter of days.”“‘Dynamic Force Employment’ makes our activities unpredictable to adversaries while maintaining strategic predictabilities to our allies and partners,” the spokesperson added.The THAAD is designed to protect against hostile incoming threats such as tactical and theater ballistic missiles at ranges of 200 km. and altitudes of up to 150 km. intercepting exo-atmospheric and endo-atmospheric missiles.The system can also provide the upper tier of a layered defensive shield alongside lower and medium-tier systems, such as the Patriot missile defense system, which in the hands of the Saudis has failed spectacularly against even modest threats.Riyadh began talks to acquiring the THAAD under the administration of President Barack Obama in 2011 and the letter to formalize the procurement of 44 THAAD launchers, missiles and related equipment were signed in November, Reuters reported.The THAAD is also being used in the UAE and Oman also announced its intention to purchase the system in 2013, though the final sale has not been concluded. The THAAD is also being used in South Korea, Japan and Taiwan to protect against the threat posed by North Korea.Iran, which possesses over 1,000 short- and medium-range ballistic missiles, is suspected of continuing to smuggling weapons to countries and non-state actors such as Hezbollah, which is assessed to have an arsenal of between some 100,000 and 150,000 missiles on Israel’s northern border, and Hamas in the Gaza Strip. The Houthis, which are armed by Iran, have also fired several ballistic missiles into Saudi Arabia, including one which targeted the Saudi capital Riyadh a day before US President Donald Trump visited the kingdom.Relations between Iran and Saudi Arabia are at their worst in years with both accusing the other of subverting regional security. In comparison, while Israel has no official ties with Saudi Arabia, the relationship with the Sunni kingdom and other Gulf States has grown stronger in recent years, due in large part to the shared threat of Iran’s expansion across the region.According to Rubin, the purchase of the THAAD system by the Saudis is in Israel’s best interest.“It’s a good thing for the Saudis to have it,” he told the Post, stressing that “they have the right to defend themselves and it is not against Israeli interests that they defend themselves."