Is it possible to serve in multiple branches of the military ?

I started Coast Guard and went Army (which you don't hear often, usually it is the other way). I have met a few three branch guys as well.

I served in the Navy and the Army. Served with a bunch of guys who had multiple tours with other branches, Marines to Army, Army to Navy, Air Force to Army etc. At least that was possible from the 1960s to the 1990s. Guess they still allow it.

I did it USMC 1968-1970/Active USMCF 1973-76. Move & Join New York Army National Guard 1977-2006. You be surprise at how many former Marines did that.

Here is the thing about MOS's as being apart of a company in the force and how valuable you become can be a doable edge sword as you try to move up the chain of command. You are in line and have to wait your turn at gathering another MOS . If your request is out side the box and not one that is that companies mission you would have to transfer to and different unit or force to be a universal soldier as did I. After 21 years and 5 different Army divisions and Air Force out my job list is 11 MOS's . added to 20 years building America including miles of I-75, lakes ,ponds bridges ,homes and helping others is a way of life and you will never be without work.
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As a Navy Hospital Corpsman I served in the Navy: boot camp, hospital corps school and naval hospital at Camp Pendleton MCB. Then I went to field medical service school and served in Vietnam wit Marine Air Group-16, 1st Marine Air Wing, where I flew MedEvac. I had a full Marine Corps sea again and full Navy seabag.

#airforce won't take prior service. Navy does under certain conditions. Marine corps will but you'll have to go through basic all over again

I entered the Air Force 28 May 75 and served 4 years as a Twin-Engine Jet, Aircraft Maintenance Specialist. (Crew Cheif) I then wanted to cross train and the AF said no. I checked with an Army recruiter and was trained in Attack Helicopter Weapons Electronics and served an additional 6 years. I am now employed as an Industrial Machinery Mechanic repairing machines that produce large diameter Steel Pipe for the Oil and Natural Gas industry.

Yep. U.S Army Vietnam, Combat engineer, artillery,- California NG, Medic, Clinical Spec.-USNR, Corpsman,-USAFR, Crash & rescue Fire Fighter, Utah National Guard, Medic, Clinical Spec., USAR, Clinical Spec.

I served in the Army from 7/1966 to 5/1975 and went into the Navy from 10/1976 to 1/1988 and retired. I was in the Army Reserve in between. My last Mos in the Army was 17K40 and the Navy recruiter said it crossed over to the OS rating in the Navy but after I went in as an O/S 2 I found out it wasn't even close. 17K is a Doppler type Radar and is closer to the Fire Control Tech rating. I had fun though. I retired an OS1

i was a cpl in the marines e-4 in the marines is equivelant to the army e-5. i had more under me as a e-4 then most army e-5s. more responsibility more authority and more respect from my command. huge slap in the face going into the army. zero respect for lower ranks. e-5 didnt respect the job you did no matter how good it was. it was an utter shock on how the army worked.