Direct commission: civilians who have special skills that are critical to sustaining military operations and supporting troops may receive direct commissions. These officers occupy leadership positions in law, medicine, dentistry, pharmacy, intelligence, supply-logistics-transportation, engineering, public affairs, chaplain, oceanography and others.
I have already served in the military years ago. But I wondered if there was a primer that might have helped me improve my test scores. I think this book would help. Unfortunately it's hard to learn enough from a book to do well on the math and reading comprehension of the ASBAB test. Study hard in math and English class in high school. It's hard to cram from a book to pass a comprehensive test that covers many topics. I think it may give you a few extra points, however.

After adopting the test in 1976 the test became a way of indicating whether or not an individual was 100% qualified to serve. As previously mentioned this aptitude test has a colorful history. That is because it underwent a dramatic change in 2002 and another dramatic change in 2004. The change that occurred in 2002 expanded the categories of the test and the overall difficulty. This can be seen by the addition of all of the diverse categories below:
Mathematics Knowledge tests the ability to solve problems by applying knowledge of mathematical concepts and applications. The problems focus on concepts and algorithms, and involve number theory, numeration, algebraic operations and equations, geometry, measurement and probability. Mathematics Knowledge is one factor that characterizes mathematics comprehension; it also assesses logical thinking.