Earlier, Gordon Adams, a military analyst at American University, told The Fiscal Times that the mission to stop ISIS will cost $15 billion to $20 billion annually, based on his “back of the envelope” calculations. The estimated $30 billion to $40 billion of new spending would come on top of the Pentagon’s $496 billion fiscal 2015 operating budget for personnel and contractors and the roughly $58.6 billion in an “Overseas Contingency Operation” fund that is used to finance U.S. The OCO, as it is known, has paid for the protracted U.S.