On this day: April 4

De Havilland Comet Enters Commercial Service, April 4, 1952

On April 4, 1952 the de Havilland Comet became the first commercial jet airliner to enter scheduled passenger service, inaugurating a new era in faster postwar air travel while also prompting rapid advances in aviation design and safety scrutiny.

First Permanent Artificial Heart Implanted in 1969 Patient

On April 4, 1969, surgeons implanted one of the earliest permanent mechanical hearts in a patient with end-stage heart failure, marking a contested milestone in the development of cardiac prostheses and long-term mechanical circulatory support.