During a three-year period the Educational Testing Service has carried on a research program for the U.S. Naval Postgraduate School for the purpose of developing a test to be used as part of the means of selecting students for the School. Three experimental test batteries have been developed during this period and tried out at the School. In addition, a five-part aptitude test was administered in 1948 "in the fleet" to applicants for admission to the School. All tests have been evaluated against criteria of academic success at the School. In addition, 1948 tests have been judged for effectiveness in predicting continuation at the School. Accumulated validation data led to the recommended test, which consists of Mathematics Aptitude, Advanced Mathematics, Physical Science and Engineering, Interpretation of Scientific Data, and Experimental Science sections. The recommended test can confidently be expected to be of significant value in determining which of the applicants are most likely to succeed in their work at the Postgraduate School.