I believe you are incorrect about the US Army’s percent of the federal budget. Total defense spending (all branches) represents around 15% of the budget.
Source: https://en.wikipedia.org/wiki/Expenditures_in_the_United_Sta...
Source: https://en.wikipedia.org/wiki/Expenditures_in_the_United_Sta...
I was looking at the discretionary budget breakdown: https://www.pgpf.org/chart-archive/0070_discretionary_spendi...