https://www.goarmy.com/about/what-is-the-army/history.html

Founded: June 14, 1775

Birthday: June 14

The First Military Branch of the US Armed Forces

Origin: Continental Army during the Revolutionary War.

https://www.history.navy.mil/browse-by-topic/commemorations-toolkits/navy-birthday/OriginsNavy/the-birth-of-the-navy-of-the-united-states.html

Founded: October 13, 1775

Birthday: October 13

Though commonly thought founded same time as the Army, it actually is the second branch to come into the Armed Forces, months after the Army.

Origin: Continental Navy during the Revolutionary War.

https://www.afspc.af.mil/News/Article-Display/Article/942428/a-brief-history-of-the-us-air-force/

Founded: September 18, 1947

Birthday: September 18

The Air Force was once a section of the US Army during WW1 & 2, only becoming an official branch of the Armed Forces after World War Two.

Origin: Aeronautical Division of the US Signal Corps, founded in 1908.

https://www.military.com/military-appreciation-month/origins-of-marine-corps-day.html

Founded: November 10, 1775

Birthday: November 10

Became its own branch on July 11, 1789, 24 years later after it's founding.

Origin: Continental Marines during the Revolutionary War.

https://www.spaceforce.mil/

Founded: December 20, 2019

Birthday: December 20

The idea of the Space Force being a separate branch came in 2017, 2 years before its official founding.

Origin: Air Force Space Command, formed September 1st, 1982.