It was between April 6 and September 28, 1924, that the first flight around the world was made. Four Douglas Cruisers, each carrying two men, started the flight from Seattle, Washington. A world-wide organization was set up to service the planes as they circled the globe. Two of the planes completed the trip 175 days later. The total distance flown was 26,345 miles and the total flying time was 363 hours, 7 minutes. A third plane was destroyed in a crash in Alaska early in the flight, and the fourth sank after a crash in the Atlantic on the last lap of the trip. The DWC’s used in the flight were powered with 450-horsepower _Liberty_ engines, and the average speed was about 72 miles per hour. This round-the-world flight was truly a daring operation. [Illustration] AIR PROGRESS In the early twenties the design of the airplane underwent very little change. The biplane with an enclosed fuselage remained standard in both military and civil aircraft. With the exception of a few Navy flying boats, the biplane was a two-place plane capable of carrying the pilot and one passenger, or 300 pounds of cargo or mail. There were some attempts at streamlining to eliminate drag, but they consisted mainly of using fewer wing struts and wire bracings. Landing gears were made stronger and the oleo landing strut was introduced. The oleo landing strut was made by two sleevelike cylinders which operated as does a piston. The upper cylinder was filled with heavy oil. The landing wheels were attached to the lower cylinder. On landing, the weight of the airplane caused the cylinder to push up, as a piston, into the oil-filled upper cylinder. This produced a pressure on the oil. A small opening in the cylinder allowed the oil slowly to slip out of the cylinder. This reduced the pressure gradually as the gear absorbed the landing shock. If you take a bicycle pump and hold your finger over the valve, then build up pressure in the pump and at the same time allow just a little air to escape from under your finger, you will readily see how the oleo landing works. The oleo shock-absorbing type of landing gear is standard with all modern planes. Fuselage construction of wooden stringers and posts, with the wire bracing so familiar in all early airplanes, gave way to the use of veneered wood covering. The first Douglas planes, the DH-4’s, the Curtiss Orioles, and the L. W. F. of the early twenties used veneer covering instead of fabric for their fuselages. This was followed by the introduction of welded steel tubing for fuselage framework. Several attempts were made to develop a monoplane in those days but none was very successful. In Germany, in 1922, the Junkers JL6 was the first plane successfully to use an internally braced monoplane wing. In this country it was several years before an aircraft designer dared to attempt to overcome the prejudiced aviators against the monoplane design. [Illustration]