Pratt & Whitney JT3D no. 1 and 2. Note different pylons (absention of turbocompressor at no. 1), the closed large "blow-in" doors and partly opened Krueger flap.
This KC-135A have interested history. Manufactured in 1957, used in experiments to determine effects of Aurora Borealis on radio communications in 1957/58, later used in nuclear weapon test programs, wfu to AMARC 28.04.1993 after TT 14062 hours.
One of three built EC-135J Silver Dollar. Heavily-modified as an electronic warfare aircraft and command post at nuclear conflict. Its successor is E-4B.
