Clarence Duncan Chamberlin (November 11, 1893 – October 31, 1976) was an American pioneer of aviation, being the second man to pilot a fixed-wing aircraft across the Atlantic Ocean, from New York to the European mainland, while carrying the first transatlantic passenger.

Clarence Duncan Chamberlin was born on November 11, 1893, in the small town of Denison, Iowa, to Elzie Clarence and Jessie Duncan Chamberlin. Elzie, or "EC" as he was known around Denison, was the local jeweler and the owner of the first automobile in Denison. This automobile was notorious throughout Crawford County for the racket it emitted while in operation. Indeed, maintenance of the vehicle was a near constant endeavor; however, it was in maintaining the family automobile that Chamberlin first developed an interest in all things mechanical. Additionally, he found great delight in using his mechanical skills to repair the clocks and watches that would be brought into his father's jewelry shop on an almost daily basis. It was also in Denison that Chamberlin would see his first airplane, an early pusher type plane, which had put on a show for a Firemen's Convention that had been held in Denison. From that moment, a desire grew within Chamberlin to one day take to the skies.

After completing his education in the Denison Public Schools system in 1912, he enrolled at the Denison Normal and Business College. While at Denison Normal and Business College, Chamberlin took college prep courses to help him in his pursuit of a degree in Electrical Engineering at Iowa State College in Ames, Iowa. During his time at the college, in addition to his classes and in order to pay for those classes, Chamberlin worked nights as a tender for the Ft. Dodge, Des Moines, and Southern Railroad Company in the railroad's electrical power sub-station in Ankeny, Iowa. In order to do this, Chamberlin found himself forced to live on trains, where he would study, eat, and sleep during travel between work and classes. However, in 1914, Chamberlin, as a college sophomore, left Denison Normal and Business College, to run a Harley-Davidson dealership in town.

Under the control of Chamberlin, the Harley-Davidson dealership thrived. As the owner of the dealership, Chamberlin had the opportunity to utilize his mechanical knowledge to both repair and sell the motorcycles. In 1915, Chamberlin was offered a job by Charles W. Tabor, one of Denison's more prominent citizens, to serve as a chauffeur on a six-month trip through the southwest and to San Francisco for the World's Fair.

It was on this six-month trip that Chamberlin would discover (and rediscover) two of his lifelong loves. In addition to meeting Wilda Bogert of Independence, Iowa, who would later become his wife; it was in San Francisco that Chamberlin would rediscover his passion for flying. It was in San Francisco that Chamberlin saw his second airplane, an early style flying boat that was carrying passengers at $25.00 per head. When he told Tabor of his intention to take a ride on the plane, Tabor replied "You can risk your fool neck in one of those some other time, but right now I've got a lot more places on the coast that I want to visit, what's more, I don't intend looking around for another driver to get me back home." While the opportunity was lost, the passion was not.

When he returned to Denison in 1916, he expanded the motorcycle business by adding a line of REO automobiles and Diamond tires to his dealership. In addition to hiring two more staff members, Chamberlin added a service station for cars, motorcycles, and tire repair. Tire repair ended up being the most profitable aspect of the business.

In 1917, Chamberlin decided to finally pursue his dream of flying. On Thanksgiving Day, he traveled to Omaha where he enlisted with the Army Signal Corps as an aviator. However, he was told that aviation was too crowded at that time, and he was encouraged to pursue a career as a military balloonist. Chamberlin declined; he didn't want to float, he wanted to fly. Returning to Denison, he waited for a position to open up at the military's flying school. His dream to become an aviator would finally come true on March 16, 1918, when he received orders to report to the School of Military Aeronautics at Champaign, Illinois, where the Aviation Ground School had been established at the University of Illinois.

Following his time at the Ground School, he reported to Chanute Field, Illinois, where he continued his aviation education. Chamberlin's flying ability progressed rapidly under the tutelage of his military instructors and on July 15, 1918, Chamberlin received a commission as a 2nd Lieutenant in the Army Signal Corps. Soon after his promotion he became an instructor himself until November 1, 1918, when he received orders to proceed to Hoboken, New Jersey, where he would await his deployment overseas. When he arrived in Hoboken on November 11 he was greeted by the news that the Great War had ended.