Each service has a uniformed head who is considered the highest-ranking officer within their respective service, with the exception of the chairman and vice chairman of the Joint Chiefs of Staff, and the chief of the National Guard Bureau. They are responsible for ensuring personnel readiness, policy, planning and training and equipping their respective military services for the combatant commanders to utilize. They also serve as senior military advisors to the President, the Secretary of Defense, their respective service secretaries, as well as other councils they may be called to serve on. They are as follows:

Limited Duty Officer: due to the highly technical nature of some officer billets, the Marine Corps, Navy and Coast Guard employ a system of promoting proven senior enlisted members to the ranks of commissioned officers. They fill a need that is similar to, but distinct from that filled by warrant officers (to the point where their accession is through the same school). While warrant officers remain technical experts, LDOs take on the role of a generalist, like that of officers commissioned through more traditional sources. LDOs are limited, not by their authority, but by the types of billets they are allowed to fill. However, in recent times they have come to be used more and more like their more-traditional counterparts.
Your success on ASVAB test day depends not only on how many hours you put into preparing, but also on whether you prepared the right way. It’s good to check along the way to see whether your studying is paying off. One of the most effective ways to do this is by taking ASVAB practice tests to evaluate your progress. Practice tests are useful because they show exactly where you need to improve. Every time you take a ASVAB practice test, pay special attention to these three groups of questions:

I don’t mean just being present. I’m talking about large-scale military deployments — the sort that would be necessary to respond to North Korean or Iranian aggression, or to fight alongside our NATO allies should one of them invoke Article 5. The threat of an overwhelming American force is the deterrent that keeps many of our foes from pushing the envelope as far as they’d like.

The IRT model underlying ASVAB scoring is the three-parameter logistic (3PL) model. The 3PL model represents the probability that an examinee at a given level of ability will respond correctly to an individual item with given characteristics. Specifically, the item characteristics represented in the 3PL model are difficulty, discrimination (i.e., how well the item discriminates among examinees of differing levels of ability), and guessing (i.e., the likelihood that a very low ability examinee would respond correctly simply by guessing).