Each unit of the national guard showing attendance and actual drill of those present for such drills as are prescribed in compliance with the National Defense Act or its amendments and such regulations as prescribed by the secretary of defense, shall receive an annual allowance for military purposes, in the sum of five dollars per capita, to be paid in semiannual installments on the basis of two dollars and fifty cents per capita. For the purpose of computing each semiannual installment the per capita strength shall be the average enlisted strength of the unit, for that semiannual period; however, if the average attendance of any unit during any semiannual period falls below fifty percent of the average enlisted strength of such unit in that period, the allowance shall not be paid for that period. The semiannual periods shall begin January 1 and July 1. The allowance shall be paid from the funds appropriated for the support and maintenance of the national guard, and the adjutant general shall prescribe regulations requiring an itemized statement of the allowance and governing its expenditure. The allowance shall be used for morale purposes and for the welfare of the troops. The allowance shall not be used to purchase an alcoholic beverage or beer.