CAT stands for computerized adaptive testing. It is a method of delivering tests by computer in such a way that it tailors the difficulty of the test to your level of ability. For example, very high-ability examinees receive difficult questions (not wasting time on easy questions), while low-ability examinees receive easier questions (not being discouraged by questions that are far too difficult). This has many advantages, the most obvious of which is that the test feels more appropriate for any given examinee. But the most important advantage is that CAT typically cuts testing time in half by eliminating items that are completely unnecessary for a given examinee.
What does this mean for you? Do not expect an experience like a traditional “fixed-form” test, where everyone receives a large number of items with a wide range of difficulty (some easy, some hard, some medium). Because items are matched to your ability, they will all seem moderately difficult. Because of this, a CAT might actually feel more difficult than you are used to – but do not worry, the sophisticated scoring system used by the CAT-ASVAB always takes difficulty into account, leading to extremely accurate scores.
Also, do not worry that other examinees saw different test questions; the military conducts extensive scientific research and statistical analysis to ensure that the test scores are as fair as possible. In many ways, a CAT is actually more fair; it reduces time wastage and item “overexposure,” as well as producing more precise scores than a traditional fixed test containing the same number of questions.