Keeping a 1960s airframe relevant in the 2050s has less to do with nostalgia than with wiring diagrams, test cards, and the unglamorous reality that engines wear out. That is the context for the U.S.

The Air Force awarded Boeing a $2 billion contract to start replacing the first two Stratofortress's engines with new Rolls-Royce engines. (Tech. Sgt. Codie Trimble/Air Force) In December the Air ...