A refusal by the United States to allow Israel to repair computer systems in the Joint Strike Fighter (JSF) is at the heart of disagreements between the Defense Ministry and the Pentagon that have been holding up an official Israeli order for the fifth-generation fighter jet. The JSF, also known as the F-35, is a stealth fighter jet under development by Lockheed Martin. Last year, Israel received approval from the Pentagon to purchase up to 75 aircraft in a deal that could reach close to $20 billion. Defense officials told The Jerusalem Post on Thursday that talks between the Israeli defense delegation in Washington and the Pentagon have picked up speed in recent weeks but have yet to result in agreement due to the US's refusal to grant Israel access to the plane's internal computer mainframe. The Americans are concerned that by allowing Israel to independently repair the computers, the Israel Air Force will get its hands on the classified technology that was used to make the plane. Israel, on the other hand, has argued that due to its operational requirements it needs to have the ability to repair damaged or broken computer systems in "real time" and cannot wait for a computer system to be sent to the US for repairs in the middle of a war. The Americans have told Israel it will receive a number of spare computer systems that it could install in place of a damaged system but would still have to send the damaged system to the US for repairs. "This is the core of the disagreements right now," explained one senior defense official. "We have major operational constraints and need to have the ability to repair the systems on our own." Due to the disagreements regarding the computer, as well as American opposition to the integration of Israeli systems into the plane and its overall soaring cost - now reaching $100 million - the Defense Ministry has recently asked Boeing for details on the new and advanced model of the F-15 Eagle, which is claimed to have enhanced stealth capabilities. There is also an option to upgrade existing F-15s to the Silent Eagle model at a much lower cost. In March, Boeing unveiled the F-15 Silent Eagle (F-15SE), a new configuration of the F-15 which has undergone improvements and modifications that, according to media reports, give the plane a stealth capability that is effective in evading radars on enemy aircraft but not against ground-based radar systems. Improvements in stealth include coatings and treatments to the aircraft, as well as a new design for the conformal fuel tanks that includes the possibility of carrying weapons inside them instead of fuel. Israel operates several squadrons of F-15s, including one of 25 F-15Is, the aircraft with the longest-range in the IAF.