An indication (the "safe separation" part) that using a proven civil design for military use isn't always that simple? I don't know if this was an issue in the case of the P-8, but maybe the USN and USAF have different approaches?
737 goes to war - the P-8A Poseidon
Boeing's original proposal was to buy a 737-800 off the commercial line, fly it a modification centre, take it apart and put it back together - as it does with the airborne early warning and control 737 and KC-767 tanker. "We have always built a green aircraft and modified it because it is difficult to do in line," says Perry Moore, director of P-8 manufacturing operations for Boeing Commercial Airplanes. "But the navy wanted us to find a way to do this.
"The navy said why buy a good aircraft and cut it apart? If you do not do something different, you will probably not win the contract," says Eric Lindblad, director, P-8 aircraft systems. "We had to take a high-powered production machine and learn how to make a military derivative."...........
Final assembly of the P-8 could have been performed on the existing 737 moving lines at Renton, but Boeing decided it less risky to create a separate line. It would also be easier to meet the Pentagon's security restrictions by building a separate "ITAR compliant" line that would nonetheless be available to build commercial 737s if Boeing needed more capacity.
"The real significant difference is in final assembly, and it was not worth the risk of disrupting the commercial line," says Moore. "We have a new final assembly line, but it's another commercial line, a replica of the others with the same lean production system. It's a moving line, but with extended flow times." Almost four times the number of wiring bundles in a typical 737 have to be installed, along with extra ducting and the cargo-bay auxiliary fuel tanks. "The line will not move as fast,"...........