Bell X-2 Formerly XS-2

Douglas X-3 Stiletto Formerly XS-3

Northrop X-4 Bantam Formerly XS-4

Bell X-5 Formerly XS-5

Convair X-6 Projected nuclear-power research variant of B-36

Lockheed X-7

Aerojet General X-8 Aerobee

Bell X-9 Shrike

North American X-10

Convair X-11

Convair X-12

Ryan X-13 Vertijet

Bell X-14

North American X-15

Bell X-16

Lockheed X-17

Hiller X-18

Curtiss-Wright X-19

Boeing X-20 Dyna-Soar

Northrop X-21

Bell X-22 Model D2127

Martin Marietta X-23 PRIME

Martin Marietta X-24

Bensen X-25

Lockheed X-26

Lockheed X-27 Lancer

Pereira X-28 Osprey I

Grumman X-29

Rockwell X-30 NASP

Rockwell/MBB X-31 EFM

Boeing X-32 JSF

Lockheed Martin X-33

Orbital Sciences X-34

Lockheed Martin X-35 JSF

Boeing X-36

Boeing X-37 Future - X

Scaled Composites X-38 Lifeboat

X-39

Boeing X-40 SMV

X-41

X-42

MicroCraft X-43 Hyper-X

L.Martin/Boeing X-44 MANTA

Boeing X-45 UCAV