The first military specification which defined all physical and operating parameters of a circular connector, AN9534, appeared on November 1, 1934. This specification was superseded two years later by AN-W-C-591, which was used with various revisions for the duration of World War II. The growing importance of airpower during the war led to the establishment of the U.S. Air Force as a separate branch of the military with a whole new set of connector requirements.

In 1949, MIL-C-5015 superseded AN-W-C-591 and became the first coordinated connector specification approved for use by all three services, Army, Navy, and Air Force. Considered the “Granddaddy” of all connector specifications, MIL-C-5015 covers power connectors available in contact sizes from 16 to 0 and operating voltages ranging from 200 to 3000 volts AC (rms). Initially, these connectors did not include environmental sealing and were available only with solder contacts. Class “M”, a moisture-resistant version, soon appeared but was superseded by Classes “E”, “R” and “F”. The environmental characteristics of the connector improved with each new class. Revision F became effective in 1971 and unified accessory thread configurations and also added a rear release crimp contact connector known as the “3450” series. The current revision is Revision G which clarifies definitions, testing, and operating requirements.