Personnel may be recruited or conscripted, depending on the system chosen by the state. Most military personnel are males; the minority proportion of female personnel varyies internationally (approximately 3% in India,[8] 10% in the UK,[9] 13% in Sweden,[10] 16% in the US,[11] and 27% in South Africa[12]). While two-thirds of states now recruit or conscript only adults, as of 2017 50 states still relied partly on children under the age of 18 (usually aged 16 or 17) to staff their armed forces.[13]
In the 1950s, the military adopted a single exam known as the Armed Forces Qualification Test (AFQT). Used as a screening tool, the AFQT measured a recruit’s ability to absorb military training and their future potential. It was supplemented by service-specific battery tests for the purposes of MOS classification. In 1972, the Department of Defense determined that all services should use one exam for screening and assigning individuals to an MOS. The AFQT was phased out over a two-year period in favor of the current Armed Services Vocational Aptitude Battery (ASVAB) test.
After adding so much information to the aptitude test, there was a bit of difficulty interpreting the test results. In addition to that, a vast majority of test takers were deemed as being under qualified based on their test results. This is why the percentile change was made. It ensured that a 50% actually correlated with a person doing better than 50% of the test takers. Those revisions have worked hand-in-hand with the preparation of the armed forces.

This continued in the 19th century, with publications like Punch in the British Empire and Le Père Duchesne in France, poking fun at the military establishment. This extended to media other print also. An enduring example is the Major-General's Song from the Gilbert and Sullivan light opera, The Pirates of Penzance, where a senior army officer is satirised for his enormous fund of irrelevant knowledge.
Again, the ASVAB is a wide-ranging exam covering many different areas. The designers of ASVAB practice tests, at least the high quality ones, know this and have spent time researching past tests to come up with practice tests that feature questions covering areas commonly tested for on the real exam. Thus, taking practice tests is a great way to focus on the material that matters most and avoid wasting your time studying content that likely won’t be on the test.
After World War II, with the onset of the Cold War, the constant technological development of new weapons was institutionalised, as participants engaged in a constant 'arms race' in capability development. This constant state of weapons development continues into the present, and remains a constant drain on national resources, which some[who?] blame on the military-industrial complex.
The scores from the other tests are used to determine what type of specialty you might be best suited for.  These "composite" scores (also known as line scores, MOS scores, or aptitude area scores) are calculated by adding together combinations of the different sub test standard scores. These composite scores are then used to determine which different military jobs (aka Military Occupational Specialties or MOS) may be the best fit for you.  Each branch of the military will have their own approach to these composite scores.
The ASVAB is a series of timed aptitude tests that are used to classify selected candidates into appropriate job roles as well as ultimately decide the eligibility of candidates for US military service.  In other words, perform poorly on this test and you could severely limit your opportunities in the military or even prevent yourself from serving.
Test scores provide only one measure of your skills and abilities.  Test scores and grades, combined with information about your interests, values, skills, and achievements may help you select appropriate occupations for career exploration.  As you explore careers, you can compare your skills with the skill requirements of occupations in which you are interested.