Mike Cummins is a part-time agent of the CIA.
By that I mean that while he has a day job that he enjoys and which is his primary focus, he occasionally gets a call from the people at Langley to assist in an unusual matter. Considering that the three recorded adventures we have of him as of this writing take place in 1975, 1978, and 1982, it is apparent that this is very infrequent and it is safe to say that Cummins is never expecting the call at any time.
When we meet him initially, he is a Lieutenant in the U.S. Navy, completing OCS in 1970. He is currently stationed aboard the USS Hull, a destroyer serving in South Vietnam in the last few months of American involvement in that conflict. Prior to that he had twice been the officer-in-charge of Swift boats operating out of Da Nang.
It is interesting to note that Cummins, still a single man and very much suited for the type of life a naval career would offer, was also finding dealing with a good number of those above him in the chain of command were really not that good at their jobs. It was starting to grate that he had to follow orders from too many people where were clearly not up to the jobs their were given. He still loved the Navy but did not know if it was for him long term.
Which might be why when the CIA came asking for help with a dangerous and exciting mission needing a Swift boat commander, he was not at all adverse to agreeing.
Nor will his willingness to be associated with the Agency, albeit usually in a remote basis, wane. The CIA, through one of its senior agents, Neil Barnett, will keep in tough with Cummins and when Cummins finally decides to leave the Service and start up successful business managing assets while living in South Carolina. Langley will even go so far as to create a cover identity for him as a South African investment banker.
The relationship between Cummins and the CIA is a good one which will be needed because when the Agency calls for his help, it is never with something simple.