Yes - WWII and Korean war - over something over 8 years total time ( about half active duty and the remainder organized reserve) I had duty with the army, Navy, Marines, and Air Force. You know how it is - some people just spend longer finding their niche in life.
If you were in a Marine Artillery Battalion in 1950 and were told this young kid was your Assistant Battalion Surgeon - would you feel more secure - or more motivated to avoid getting wounded?
As most here probably know, the USMC gets their medical services from the Medical Corps of the Navy so, while I served with the USMC, I was never actually a member of the USMC. The members of my battalion felt I was one of them, however - particularly when I enthusiastically always joined them on the firing range - hey, as a kid in depression days I had to buy my own gun and ammo - no way would I pass up their furnishing me the rifle, ammo, and range - and pay me for that time in addition!!
Many aren't aware that one of the six "Marines" raising the flag in the Iwo Jima statue was actually a Navy Pharmacist Mate 2nd Class John Bradley who was awarded the Navy Cross - second only to the Medal Of Honor. He is in the middle.
My service may have benefited my country but, in the final analysis, I was the one who benefited most form that experience and service and I'm sure most of us felt the same way.