70 years ago today, on March 21, 1955 (February 28, 1955 in the lunar calendar), Mao Zedong wrote an inscription: To build a strong air force. From March 21 to 29, 1955, the first Air Force Congress of Heroes and Model Heroes was held in Beijing. Chairman Mao sent an inscription to the conference: "Build a strong people's air force, defend the motherland, and prepare to defeat the invaders."