Almost two fifths of Army recruits have the reading level of a 11-year-old, MPs have warned.
And a similar proportion can only do maths aimed at pupils in their final year of primary school, according to a report by the Commons defence select committee.
The study, which looked at the education in the armed forces, found that the Army, Royal Air Force (RAF) and the Naval Service have a decent record in improving the maths and English skills of young recruits and trainees who join up with low levels of qualifications.
The minimum requirement of new recruits is "entry level 2", the report says - equivalent to the standard expected of a seven or eight-year-old in literacy and numeracy.
Of those who were recruited in 2012, all of those who joined the Naval Service or the RAF were above entry level 2, it found. But 39% of the Army had a literacy level of an 11-year-old, and 38% had this level of ability in numeracy.
It also found that 3.5% of the Army were reading at the level of a seven or eight-year-old, while 1.7% were at this standard in maths.
The Ministry of Defence (MoD) had told the committee that it recruits service personnel at whatever level of attainment is available, the report says, adding that if this is the case, then it should take action when entry standards are particularly low.
It says that in light of planned changes to the three services, "it may be that recruiting personnel with higher levels of attainment would better meet the future needs of the armed forces".
"The MoD should identify how it might raise the basic entry level and still recruit sufficient personnel," the report says.
The committee goes on to suggest: "Whilst we recognise that some recruits may not have done well in their previous academic careers and may not be eager to take further academic exams, the MoD should encourage more recruits to undertake English and Maths GCSEs which would stand them in good stead for future employment."