“There had been conversations for decades,” said a senior industry adviser on condition of anonymity because he was not authorized to speak with the media. “But buying the whole BAE, with golden share and other things like dual-listing, dual-incorporation structure, U.S. guys say it’s not worth it.”

For its part, BAE Systems has repeatedly said it has no intention of selling the U.S. unit, which contributes more than half of the company’s revenue.

BAE officials made clear in recent weeks that any move by the U.S. government to require divestitures as a condition for approving a merger with EADS would have been a deal-breaker.

Some sources cautioned that a new round of merger considerations involving BAE cannot be ruled out, given the challenging defense environment.

But most potential U.S. bidders have their own reasons for why the deal would not make sense right now.

Executives at Lockheed Martin Corp have said privately that they have no plans to pursue BAE, which is a key supplier on its troubled F-35 Joint Strike Fighter program. They say the company is squarely focused on its performance on the F-35, the Pentagon’s largest weapons program, and does not need the distraction of integrating a major acquisition.

Boeing is more focused on its booming commercial business and expanding its position in the cyber and unmanned systems areas at the moment, according to company executives and analysts.

Raytheon’s Chief Executive William Swanson has publicly discussed the immense challenges involved in absorbing such a large, complex company.

Northrop Grumman just sold two units, including its lackluster shipbuilding business, to streamline the company, making an acquisition highly unlikely, according to company insiders.

Chief Executive Wes Bush is more focused on creating a high-performing defense company and maintaining profit margins, not acquiring a company whose revenues have been hard hit by the downturn in demand for ground combat vehicles, according to analysts and company executives.