"The Noncommissioned Officer and Petty Officer: Backbone of the Armed Forces (2013)" states that, "To be successful in building and sustaining (a solid and trustworthy) relationship with officers, NCOs/POs must be ."

Competent, credible, and capable

Explanation:

The Noncommissioned Officer and Petty Officer: Backbone of the Armed Forces (2013) is authored by U.S. Marine Corps Sgt. Maj. Bryan B. Battaglia, and Gen. Martin E. Dempsey.

Sgt. Maj. Bryan B. Battaglia was the Senior Enlisted Advisor to the chairman, United States of America Army. Gen. Martin E. Dempsey was the chairman of the Joint Chiefs of Staff.

"The Noncommissioned Officer and Petty Officer: Backbone of the Armed Forces (2013)" states that, "To be successful in building and sustaining (a solid and trustworthy) relationship with officers, NCOs/POs must be competent, credible, and capable."

NCOs/POs being competent suggests that they are extremely expected to be technically and tactically qualified than their junior colleagues and are always ready for the call of duty.

To be credible means the NCOs/POs are required to be confidence, loyal and trustworthy.

Also, NCOs/POs must be capable of performing their duties with excellence and due diligence. They should be able to utilize their skill set, knowledge and competence experience to solve problems in the real world.

Hence, when NCOs/POs possess these three Cs (competence, credibility, and capability), they're are able to impact their units effectively and improve the quality of their subordinates.