Very good! No. 20 was pretty impossible if you haven't been there and don't know anything about field ambulances. 

1.   Spad S-13 (r, s)
 2.   Boeing Stearman PT-17 (s)
 3.   North American AT-6D Texan (s)
 4.   Consolidated B-24M Liberator
 5.   North American P-51D Mustang (r)
 6.   Douglas C-47 Skytrain (s)
 7.   Boeing B-17G Flying Fortress
 8.   Republic P-47 Thunderbolt
 9.   Grumman TBM-3 Avenger (s)
10.  Boeing B-29A Superfortress
11.  North American B-25J Mitchell (s)
12.  Lockheed SR-71A Blackbird
13.  Boeing B-52D Stratofortress
14.  Lockheed U2-C (s)
15.  North American F-100D Super Sabre (s)
16.  Bell UH-1 Huey
17.  McDonnell Douglas F-4J Phantom II
18.  General Dynamics F-111E
19.  Fairchild Republic A-10 Thunderbolt II (s)
20.  Dodge T214-WC54 Ambulance
21.  Ford M718 MUTT Ambulance