You pay no West Virginia income tax on military pay you earn while serving in the National Guard or the Reserves after being called to federal active duty for Operation Enduring Freedom, or for domestic security duty ordered by the President.
There is nothing to apply for. Leave the exempt military pay out of the income you report on your West Virginia return, and keep your mobilization orders with your tax records.
Your federal active duty orders showing the operation or domestic security mission, and your Leave and Earnings Statements for the period.