Psychologist Linda Gottfredson in her 1997 article titled, “Why g Matters: The Complexity of Everyday Life” (Intelligence 24(1) p. 90) stated:
Minimum enlistment standards since World War II have generally been higher than the 10th percentile, and closer to what they are today for the different services: the 16th percentile on the Armed Services Vocational Aptitude Battery (Army about IQ 85), 21st percentile (Marine Corps and Air Force, IQ 88) and 27th percentile (Navy, IQ 91). It should be noted that these are the enlistment standards for high school graduates. Nongraduates must score between the 27th to the 65th percentiles on the AFQT, depending on the service in question.
A more recent posting at Reference.com states: There is no minimum IQ score to join the U.S. Army, but applicants have to score at least 31 on the Armed Forces Qualification Test.
The official US Marine Corps site at ssmc.net states: Applicants must qualify for enlistment on the Armed Services Vocational Aptitude Battery (ASVAB) test. However, no minimum score on this test battery is indicated in that criterion.
One might conjecture that a minimum score might be somewhat flexible depending upon the supply and demand of recruits. However, I have found no documentation to support this conjecture.
On September 29, 2021, Michael Kraus called my attention to US Code Title 10 Armed Forces §520 that provides more precise information. This section is available at: https://www.law.cornell.edu/uscode/text/10/520 It reads:
(a) The number of persons originally enlisted or inducted to serve on active duty (other than active duty for training) in any armed force during any fiscal year whose score on the Armed Forces Qualification Test is at or above the tenth percentile and below the thirty-first percentile may not exceed 20 percent of the total number of persons originally enlisted or inducted to serve on active duty (other than active duty for training) in such armed force during such fiscal year.
(b) A person who is not a high school graduate may not be accepted for enlistment in the armed forces unless the score of that person on the Armed Forces Qualification Test is at or above the thirty-first percentile; however, a person may not be denied enlistment in the armed forces solely because of his not having a high school diploma if his enlistment is needed to meet established strength requirements.
Subsequent modifications and additions to this code are provided at the link given above.
The ASVAB is the method the US military uses to test for IQ. 10 USC §520 does not allow accepting those who score below the 10th percentile, and only 20% of the force may be below the 31st percentile
Thank you for that lead Michael. I have subsequently researched the section of the military code that you suggested and found that you are correct. Thank you. A complete statement of the relevant section can be found at: https://www.law.cornell.edu/uscode/text/10/520. It reads:
(a) The number of persons originally enlisted or inducted to serve on active duty (other than active duty for training) in any armed force during any fiscal year whose score on the Armed Forces Qualification Test is at or above the tenth percentile and below the thirty-first percentile may not exceed 20 percent of the total number of persons originally enlisted or inducted to serve on active duty (other than active duty for training) in such armed force during such fiscal year.
(b) A person who is not a high school graduate may not be accepted for enlistment in the armed forces unless the score of that person on the Armed Forces Qualification Test is at or above the thirty-first percentile; however, a person may not be denied enlistment in the armed forces solely because of his not having a high school diploma if his enlistment is needed to meet established strength requirements.