In a bid to allay Russian fears of possible US missile-defense sites in Europe, Boeing has unveiled a proposal to build a mobile interceptor missile, Reuters reported Thursday. The 47,500-pound interceptor could be flown to NATO bases when required on Boeing-built C-17 cargo planes, swiftly put up on a 60-foot trailer stand and removed when safe, according to the report. "If a fixed site is going to be just too hard to get implemented, politically or otherwise, we didn't want people to think that the only way you needed to use a GBI was in a fixed silo," Greg Hyslop, Boeing's vice president and general manager for missile defense, told Reuters at a US Army-sponsored missile-defense conference in Huntsville, Alabama. Boeing had just started briefing the Pentagon's Missile Defense Agency on the proposal, Hyslop said. The project could be completed by 2015, and would probably cost less than had been planned for the silo-based interceptors, he said. On Tuesday, the American Raytheon Corporation said it was developing a land-based version of its existing Standard Missile-3 (SM-3) that could be used to defend Europe, Israel and elsewhere. Army Lieutenant General Patrick O'Reilly, the head of the Pentagon's Missile Defense Agency, hailed the SM-3 option Wednesday and was asked about a mobile GBI, Reuters said. "That would be a significant undertaking," he said after a presentation to the conference. "But we are looking for opportunities and the SM-3 is one we focused in on because of its accomplishments." General James Cartwright, vice chairman of the Joint Chiefs of Staff, earlier admitted that the United States had made "a couple of bad assumptions" in missile defense, including the prediction that "the emergence of the intercontinental ballistic missile threat would come much faster than it did" from countries like Iran and North Korea. "The reality is that it has not come as fast as we thought it would come," Cartwright said, adding that currently, the US had the capability to intercept 15 inbound intercontinental ballistic missiles simultaneously with the 30 GBI's being placed in silos at Fort Greely, Alaska, and Vandenberg Air Force Base, California. "That's a heck of a lot more than a rogue" nation could fire, he said.