The DC-3 was introduced in 1935 in response to the improvement requirements of American Airlines for the DC-2 at that time. The DC-3 can carry up to 30 passengers and can cross the east and west coasts of the United States with just one refueling. In addition, it features the first-ever in-flight kitchen and the ability to provide beds in the cabin, bringing revolutionary breakthroughs to commercial aviation. Prior to this, all flights did not provide hot meal services, and passengers and crew members could only enjoy meals at hotels located at intermediate stations. Once there were no hotels in some underdeveloped areas (such as Africa), it was quite inconvenient.December 21, 1935. A new type of aircraft, the Douglas DC-3, capable of carrying 21 passengers at a speed of nearly 160 miles per hour, has made its maiden flight. On the basis of the DC-2 aircraft, the fuselage of this aircraft has been enlarged to increase its carrying capacity, breaking the flight speed and cargo records of various passenger planes. The DC-3 is equipped with two 900 horsepower Curtis Wright engines, greatly exceeding the power of the DC-2 engine. According to the initial requirements of American Airlines, the DC-3 aircraft should be equipped with 14 beds to compete with the Pullman train sleeper service on the railway, but other airlines require 21 seats on the DC-3.C.R. Smith, Chairman of American Airlines, said, "The DC-3 was the first aircraft to make money by transporting passengers. In June 1936, the company launched its first non-stop air service between New York and Chicago using DC-3 aircraft. By 1938, the DC-3 had become the main aircraft of all major airlines in the United States. Due to its superior performance, DC-3 has been purchased in large quantities by airlines around the world. According to reports, by the eve of World War II, over 90% of countries around the world traveled by plane using DC-3 aircraft. The DC-3 has more stable performance, lower operating costs, and e