Israel and the US are in talks regarding the possibility that America will leave several Patriot 3 missile defense systems behind, following a joint missile defense exercise that will begin next week, defense officials said Monday. The Juniper Cobra exercise will begin next week in southern Israel, where US and Israeli forces will run simulations on various threat scenarios involving missile attacks against Israel. Ahead of the exercise, some 15 US Navy ships have arrived in Israel, in addition to about a dozen transport planes that brought equipment to air force bases in the Negev. This year's drill is being described as the largest joint exercise ever held by the countries. During it they will jointly test four ballistic missile defense systems - the Israeli Arrow 2, the ship-based Aegis, the high-altitude THAAD and the Patriot (PAC) 3 systems. This is the first time that all of these systems are deployed here. Israeli defense officials said that there were ongoing talks between the sides regarding the possibility that the US would leave several of the PAC3 systems behind following the drills. "There are talks about this possibility and the Americans will likely decide to leave the PAC3 systems here after the exercise," one official said. Juniper Cobra, senior defense officials said this week, is aimed at creating infrastructure in case Israel is attacked and the US decides to send the Aegis or THAAD to bolster the Arrow. The exercise spans several days and involves hundreds of Israeli and American soldiers, mostly from the air force. The primary focus of the Juniper Cobra exercise held in 2007, for example, was integrating the lower-altitude US Patriot missile systems with the higher-altitude Arrow 2. This year, the integration will focus on improving the interoperability between the Arrow, THAAD and Aegis. Ahead of the 1991 Gulf War, the first Bush administration sent Patriot missile batteries to help defend the country against Saddam Hussein's Scud missile attacks, and last October, the second Bush administration gave Israel a farewell gift in the form of the X-Band radar, which is deployed in the Negev and is capable of detecting targets thousands of miles away, providing five to seven minutes of warning before an Iranian missile strikes.