Army Alpha was a test that was given to soldiers in the Army a long time ago to see how smart they were. The test had lots of questions that were like puzzles. The soldiers had to think really hard and use their brains to figure out the answers.
The questions were things like, "If John can carry 4 boxes at once and he needs to move 20 boxes, how many trips will he have to make?" The soldiers had to use their math skills and figure out that John would have to make 5 trips.
Once the soldiers took the test, the people in charge of the Army could see who was really smart and who might need some extra help. This helped them decide what kind of jobs the soldiers could do in the Army.
But now, the Army uses different tests to see how smart their soldiers are and what kind of jobs they can do. Army Alpha was a really important test a long time ago, but now it's been replaced by newer and better tests.