Today, the United States military has access to only nine government and commercial tankers suitable for operations abroad, but it has projected it needs at least 80 tankers to transport fuel from oil refineries to American forces during a large war. There are another nearly 60 American flagged tankers that transport cargo among American ports, but they would need to mostly stay home to keep the domestic economy running. This lack of American tankers is not a new problem, but it has grown worse since the last United States military campaigns out in the Middle East.
In those operations, American troops counted on foreign tankers to carry their fuel overseas or bought fuel from local refineries. That may not work in the future. Many of the foreign tankers the United States military would rely on are now flagged by China, which built its own fleet of tankers and influences a critical portion of the world tanker market through financing, pooling agreements, and port management. These tankers are unlikely to be available to the United States military in any future crisis where China may be the adversary or may oppose American operations.
Most of the world tanker fleet is not controlled by China, but there is still no guarantee the United States can charter them. Foreign crews, many of whom are Chinese or Russian, may not want to sail into a conflict. Further, as with the current oil glut, tankers may not be available to move military fuels because they are full of oil or other refined products.
Without the tankers, Navy ships would be stuck in port, Air Force planes would be grounded, and Army and Marine units ashore would run out of gas. American forces would lack the ability to deploy to defend our allies, sustain operations, and could lose a war.