Either the Armed Forces have a definition of the word "career" which is different from the one I'd use,or you and I are assigning different definitions to that word.
Ordinarily,those who serve honorably for at least 20 years (or less in cases of disability) are entitled to a pension.That's what I'd define as a "career".
Our definitions of "career" coincide. The confusion seems to be from the commission status.
Upon completing a career in the regular service, an officer does not resign his commission. He submits a request to be transferred to the Retired List. Upon approval of the request, the officer is no longer on the Active List. He retains his commission, appends "(Ret)" to his title, and receives a pension.
Those on the Retired List are still in the service, just not active duty. This facilitates immediate return (recall) to active duty should the need arise.