Activity of the US Navy in Turkey in the XIXth century


I'm currently working on my family tree. I discovered my great great grandfather was a member of the US Navy.

The inscription on his tombe reads :
(First Name Last Name) Lieutenant Captain in United States Navy Justice of the peace 

He passed away in Turkey (Constantinople) in 1897.

I have reasons to believe he spent time there at least on two occasions. Just before 1850 and again in the late XIXth century.

In the meantime, I know he lived in or near New York, and I guess he spent some time in Louisiana around 1860-1861 where he had a child.

So I wnoder : Could he have been involved in the Civil War while in the Navy in Louisiana ? It seems strange to me, but I don't know much about it.

Could he have enrolled in the navy at a youg age and be sent abroad in Turkey ? did the US Navy had operations over there ? And then come back to serve during the Civil War, then became a Justice of the Peace ? Does that seem plausible or totally absurd ?

I am not familiar with the US archive system, not sure where to look at to find a trace of him among the military troops.

Sorry for the improper English, it's not my native language.

Thank you in advance for any information or tip you could give me.