TOP SECRET Air 8. Air activity over Shanghai during the past two weeks has been negligible. It is thought that the Nationalists Air Force is concentrating its attacks on communication systems south and west of the city where the railway lines have been bombed on several occasions. Attacks on Changchow have also been reported. It is thought that the object of these attacks is to prevent supplies reaching Shanghai by rail and, in conjunction with the sea blockade, to isolate the city from the rest of China.