Early systems (KH-1, KH-2, KH-3 and KH-6) carried a single panoramic camera, or a single frame camera (KH-5), while the later systems (KH-4, KH-4A, and KH-4B) carried two panoramic cameras with 30 degrees separation angle. For KH-4, KH-4A, and KH-4B missions, the two cameras are referred to as fore (for forward looking) and aft (for rear looking).
