seoul south korea plan buy additional 20 f-35a stealth fighter aircraft unite state south korean newspaper report thursday less two months u.s. president donald trump announce seoul would purchase billions dollars new military equipment south korea defence acquisition program administration establish process procure 20 additional aircraft joongang ilbo newspaper report cite multiple government source 2014 south korea formally announce plan buy 40 f-35as american defense contractor lockheed martin south korea plan buy 20 additional f-35 aircraft report