The F-15E is an expansion of the two seat F-15B trainer model of the Eagle. Among the most noticeable features of the F-15E are a pair of bulbous external fuel tanks which are blended between the wings and fuselage sides. These huge tanks carry enough fuel to nearly double the normal amount carried by the basic F-15. In addition, these conformal tanks contain sensors and tactical systems and are called FAST packs. This stands for Fuel And Sensor Tactical.