While still in Kyiv, Sikorsky designed and built his first two helicopter prototypes, the S-1 and S-2. Although these early attempts were unsuccessful in achieving sustained flight, they provided invaluable experience and insights into the challenges of rotary-wing flight.

After establishing himself in the United States with his flying boat designs, Sikorsky returned to his long-held passion for helicopters in the late 1930s. He believed that the helicopter held immense potential for a variety of applications.

Sikorsky's VS-300 (Vought-Sikorsky 300) made its first free flight, marking a pivotal moment in helicopter history. This experimental helicopter featured a single main rotor and tail rotor configuration, a design that became the standard for most modern helicopters.

Building upon the success of the VS-300, Sikorsky developed the XR-4. This model was more advanced and capable, and it became the first practical American helicopter, ordered into production by the US Army.

During World War II, Sikorsky's helicopters were used extensively by the US military for rescue missions, observation, and other critical roles. This wartime experience significantly advanced helicopter technology and demonstrated their versatility.

Following World War II, Sikorsky continued to develop and refine helicopter designs, producing increasingly larger, more powerful, and more versatile machines. His helicopters played a vital role in civilian applications such as search and rescue, medical evacuation, and transportation.