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

It is possible but each time you jump you lose seniority in the job and grade. The mode rank you gain the less likely you are to be accepted into another branch without losing rank.

It is possible. I went through tech school in the USAF, with an individual that had already served in the USMC. He finished his contract with the USMC, then he joined the USAF.

I had a good friend of mine. He was a Navy Chaplain serving with a SEAL team in Central America. He continued his college and became a Surgeon and transferred to Delta. He learned some of the things he though changed while working with SEALS. Thus he finished his medical degree. Went to Brag and saw DELTA need folks who could multi task. Thus at his 10 year or so point he went Delta. His words to me were well I can do the job, fix both the internal and mental things that follow the missions. He was not complete until he could participate, and help heal. He is now retired and is a part time minister and a full time fire fighter. To each his own but I suggest you do as he did and master your primary skills.

Re: The comment on Jessica Lynch's book. You're kidding! She got into a truck accideny because the convoy got lost then they were attacked by the enemy. Had no real combat training, broke her legs and was taken to an enemy hospital. Rescued by SF soldiers then had the GALL to accept a Silver Star! PC at its worst! Correct me if I got anything wrong.
She should be an embarrassment to any soldier. I am a Marine vet and I am embarrassed for the army.

Marine Corps 4 years, Air Force 21 years. Retired as a SMSgt

Yes

Of course you can, though as others have pointed out, being flexible and changing AFSC/MOS several times may be necessary. I served 21+ years, including three combat deployments, between 1975 and mandatory age 60 retirement in 2017.
1975-1979 Active Air Force - SIGINT Analyst
1979-1980 Army National Guard -Medium Helicopter repairer
1980-1983 Active Army - SIGINT Analyst
1983-2004 Break in service for College, Defense Contractor
2004-2005 Army National Guard - Flight Operations
2005-2017 Air National Guard - Cyber Systems Operations/Client Systems
2017 Retired from the Air Force as a Master Sergeant

I served in the Army with a great XO who came from the Marine Corps. When asked why he transferred to the Army 82nd. Airborne Division, he stated he wanted to jump out of perfectly good airplanes. The Marine Corps lost a good officer, one of the best I served with. Salute!

i spent 4 1/2 years in the navy as a heavy equipment operator, was in the army as a truck driver and then 2 years in the air force as a nothing, went back into the army.

Well, this guy did four branches... admittedly it was the Reserves, but still, in theory it's feasible to hit a bunch...

https://www.stripes.com/news/20-years-4-branches-servicemember-is-part-of-exclusive-club-1.298471

BLUF; Yes. Not concurrently however. Once you complete your mandated (contracted) AD period and returned to Reserve status,you can apply for enlistment into a second branches. The recruiter for the branc your applying for has the guidelines on how to get you released from the branch you are leaving. Depending on the new branch you select however, you may need to attend that branches Initial Entry Training

Multitasking:-)Interesting !!!

I think as long as you qualify you can serve in any branch. My best friend served in the Marines, Navy Reserve and finally the Army. However, if you want to make a career of the military, I suggest that you stick to one branch and ride out a 40 year career.

Don't get ahead of yourself, figure out if you love what you do (it sometimes takes a while) and then go from there.

Yes! I had a friend who Served in 4 Branches. He started in the Navy, went into the Marine Corps, Army and finished in the Air Force. Just as long as you finished your enlistment.

Everyone has posted good advice, one thing that comes to mind is that it seems to me that the people I have known that have been in multiple branches promote slower. As with anything, some people do bust on through and promote fast anyway
I would agree that whichever branch you choose, stay with it.
Retrain and learn a new skill. The closer you are to your final date of separation (hopefully retirement), try to find a job that translates well to the outside world. Medical is one of the really good crossovers. IT has been good for people also.
Being a highly trained killer is always exciting, and a adrenaline rush, but the matching job pool is just a little small on the outside ;)
Good luck, make it fun !!

Of course. Hell, in today's military you can be two different sexes while in only one branch. The sky's the limit.

My Dad served in the Navy in WWII, and the Army during Korea....

I was in the Navy from 85-89, the Marines from 90-94, and the Coast Guard from 99-2012. The Navy wasn’t a good fit, I liked the Marine’s but I was home much to raise my children. I retired from the CG, it worked out well for me. The draw backs are starting over and learning all the particulars of the branch you’re in.

I have served in 2 branches. I served 6 years in the Active Army, 3 years in the National Guard, and then 3 more years in the USNavy Reserves, attached to the USMC. Before I changed, I did full tours in each branch. I was able to utilize the skills I had from each time in to enhance my value and knowledge. I learned new and different skills from each branch that increased my respect and comradeship for ALL of my extended family. The one thing I do regret is that when you cross over in services, you lose one to two ranks, having to "start over" going up the "rank ladder". If you're willing to go thru the training to an extent...again...go for it. But remember, that your first enlistment will make the most lasting impact on your military...and civilian life. You'll get used to doing things a certain way, and a change in branches can be a type of "culture shock". It's exciting to try and do new things, just be aware of all the aspects before you make your decision.