The Thomas Tests for Selection and Training are based on the Navy Personnel Series.  The TST series is a parallel form of the NPS tests, and therefore the results found for the original NPS transfer completely to the TST.

The TST series is a suite of ability tests, each of which demands the subject complete one type of task in each test for a relatively short period of time.  This approach ensures a number of trials at the same class of task, whose individual items differ in difficulty only within a certain range.

The tests consist of items generated in microcomputers from a programme that constrained their difficulties. These difficulties were predicated from characteristics of the items observed in performance models.  Each test contains a number of trials at one type of item and each test is referenced in this section for further appraisal.

From knowledge that some items can be made more difficult than others, the series was at first constructed at two levels, initial and advanced level. Initial entry level means that the tests are suited to school leavers who are entering the employment market for the first time, or retraining, having not first taken a college or university qualification. Advanced entry level means that items were constructed at a higher level.

However, after successful trials with two versions, a single mid-range version was devised to cover the whole spectrum from standard school leavers to executive level candidates. It underwent standardisation trials for two years before being released.  This was called the Combined Version of the Navy Personnel Series (NPS) Tests and this combined version was the prototype for the TST series.