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

I for one served in the Air Force and in the Army. My only advice, has was in my case when switching services you may lose a rank/ pay grade. I spend more time in the Air Force. (Active and Reserves). Also know when I enlisted in Army I was in the AF Reserves, after my service in the Army I returned back to my AFR unit

Become CID

Yes. My dad spent 8 years in the Marines 4 in the Air Force got out for about 10 years then joined the National Guard and retired after 13 years

Yes it is. I enlisted in the Marine Corps in 1965 and stayed till 1974. Made SSGT in Aviation Supply. Exited service and worked for a John Deere dealer in Oregon. Joined Air Force reserve in 1975 at McChord AFB. Trained as C141 load Master, made Tsgt (E-6). In late 1977 our unit was cut to nothing. I enlisted in US Army and went to FT Bliss as a Chapparal Missleman. While at Bliss I was redesignated to the Medical career field. Became a Patient Admin Clerk. Honor graduate from Brooke Army Med Center, then to Walter Reed, then Germany. Germany became a Classified Courier. For 3 yeaars drove the length and width of Germany. Next to National Training Center as OPFOR member 11B30. Then to Fort Sill. Became System Manager of hospital information systems. A job which I held for over 12 years as military and civil service. So I went from E-1 to E-6 in 3 services. Then to GS-7 and retired. Finished up as a Dr. of Health Care Administration. At 70 years of age I am still taking classes and online learning. Education is fascinating. Also volunteer with a Wolf Rescue Sanctuary several weeks each year. If you set your mind to it you can do anything.

Absolutely, and sometimes even before your contract with one is up (inter service transfer, just has to be approved by your command). I was an active Marine for 13 years, got completely out for 3 years, joined the Air Guard and then got a conditional release to the National Guard without losing any rank. Most MOS's will transfer over to other branches if you want. Each branch has their strengths/weaknesses and good/bad points, all depends on what your looking for.

I enlisted in the US Army August 1964 and was discharged July 1967, as a Radio Relay and Carrier Operator. I enlisted in the US Army Reserves in 1981 as an Instructor and was given my rank of Sgt E-5 when I enlisted, after one year of enlisting I was promoted to E-6. In June 1983 I transferred to the Air Force Reserve as a Chaplain Assistant and kept my paygrade of E-6. I served in the USAFR as a Chaplain Assistant until I retired on May 7, 2003 when I turned 60 years of age. I also served on 2 Navy Ships as a civilian instructor teaching College Algebra, USS Mitcher and USS Bataan. While on the Mitcher I also the Lay Religious Leader and was presented a Letter of Appreciation by the Captain in the Bay at Mykonos, Greece. While on the Bataan I roomed in the Marine section and roommates were the 2 Hoover Craft pilots.

Yes, I have served honorably in both the Army and Marine Corp.

It is possible but you will generally lose rank or gain rank slower. My brother first went Army National Guard and went as far as SGT. He transitioned to Air Force and had to take a cut to E-3. He got as far as SSgt/E-5 again. He then transitioned back to SPC/E4 in the regular Army again making SGT/E5. He then had enough of the military after about 14 years and transitioned to US Air Force reserve. Went to about three drills, hated everything that was going on and went AWOL. He then went through UCMJ and received a discharge. He wasted a good chunk of his life and ruined his military reputation in the end. If he would have stayed Regular Army or Air fForce he probably would have attained E7 rank and had a decent retirement. Now he has none, but he is a vet.

What are the two services tha you are interested in changing your lifestyle for? I am a dual service member USMC/Army.

I would concur with some of the others, while it may be possible moving to many times will limit your advancement potential and with the more rank you gain the more control you have. I would say in order to satisfy your desire to expand your horizons, get into an interesting area like intelligence or something like that there are a lot of disciplines and assignments within that area that will give you exposure to other disciplines while you hone your own. That way you grow and learn at the same time and it is interesting. Of course you won't be able to talk about it but you will enjoy.