Belgium, Denmark, The Netherlands and Norway—four NATO nations acting as a consortium—will buy more than 350 new jet fighters to replace warplanes bought in the 1960s.

Europeans call it the arms deal of the century—and they may well be right. Some time this year, Belgium, Denmark, The Netherlands and Norway—four NATO nations acting as a consortium —will buy more than 350 new jet fighters to replace warplanes bought in the 1960s. France and the…