China's third airmail issue of 1932-1937 is depicting a Junkers F-13 monoplane over the Great Wall (Nankou - Pass). The series of 10 stamps were issued in three stages (29.8.1932, 13.5.1933 and 16.6.1937). The stamps are existing as Beijing prints (1932-1937) and Hong Kong prints (1940/1941). Surcharched and overprinted stamps are also existing.
The images above show the difference between the Beijing (left) and Hong Kong (right) printings, which mean the original and redrawn «piao» character. Michel and Scott catalogues refer to as the secret mark. Some philatelists distinguish also between narrow and wide stamps & missing, thin and thick bottom lines.
China 1932 - 1937, Beijing Prints
1940 Hong Kong Prints
The Hong Kong prints are existing on watermarked and unwatermarked papers.
1941, Shanghai and Nanking Air Post Stamps
Surcharge in Japanese currency, because the air main then was carried by Japanese planes.
Surcharge 10c airmail fee for postcard within the nation has been paid
Surcharge 20c airmail fee for letter within the nation has been paid
Unwatermarked & perforation 12½
The 20c overprint is existing on watermarked stamps (perforation 13) as well.
Surcharge 18c and 25c airmail fee for postcard to Japan has been paid
Surcharge 35c airmail fee for postcard to Japan has been paid
Additional surcharge in red
Sinkiang's 1943-44 provincial airmails
Several values of the Beijing and Hong Kong prints are also existing as "Sinkiang" handstamped overprints.
(note: forged stamps existing).
1945 Anti-Bomb Airmail Stamps
(Issue as air raid preauction propaganda)
1946 Inflation surcharged stamps, Beijing Print
$53 on 15c & $73 on 25c
(note: forged stamps of the $73 on 25c stamp are existing).
1946 Inflation surcharged stamps,
Hong Kong Prints
(existing on watermarked and unwatermarked paper)
1948 Surcharged stamps
The 10000 on 30c stamp is existing on watermarked and unwatermarked Hong Kong prints
The 50000 on $1 stamp is existing on Beijing prints and unwatermarked Hong Kong prints.
Other stamps existing on unwatermarked Hong Kong prints.