In the event of all-out war on the Korean peninsula, the United States would be hard-pressed to move troops and weapons to the battle after one month because of an overreliance on commercial air and sea transport, Congress was told Tuesday.

The U.S. military has enough planes and ships to flow forces into the war zone for 30 days, but after that it would become difficult because of the inability to send commercial vessels into a contested war zone, said Air Force Gen. Darren McDew, commander of U.S. Transportation Command.

In testimony before the Senate Armed Services Committee, McDew said he has been closely coordinating with Army Gen. Vincent Brooks, the U.S. Korea commander, about what he would need in the event of war against the North.

"We have a sufficient force today, and I have talked to Vince Books and his staff, to provide him what he needs in the first 30 days organically," McDew said.

Committee Chairman Sen. John McCain, R-Ariz., expressed concern about the shortage of military ships and the possible impact on a conflict.

"We are reliant to a larger and larger degree on the private-sector companies, and there are great questions among many experts that we do not have the capability, say in Korea, say in eastern Europe, to resupply and maintain our ability to carry out success in combat," McCain said.

McCain cited a Pentagon statistic that it would take 200 flights of C-17 cargo planes to move one Army brigade combat team and its equipment to Korea.

"It is not easy," McDew said, "but we can do 200 C-17 sorties."

"That gives you one brigade combat team," McCain scoffed. "I doubt if there is conflict in Korea that one brigade combat team would be sufficient for us to reinforce our forces on the ground."

"We do not have the capability I wish we had," responded McDew. "The initial force can be brought by organic fleets, and then we would have to see what we can do after that."

"Well general, to quote, 'see how we can do after that,' is not comforting to this committee," McCain said.

McDew testified that the U.S. military cargo ship fleet is "aging out" and asked Congress to approve the purchase of used commercial vessels as a stopgap measure until new military ships can be built.

The Pentagon says the average age of the Military Sealift Command's "surge fleet," needed for rapid response in a crisis, is now 39 years, and that over a recent five-month period fewer than 60 percent of sealift ships were able to activate during planned exercises due to various maintenance problems.

"A look at sealift, for example, reveals the same downward spiral we've seen elsewhere in the military: Budget cuts mean fewer new ships, existing ships get older, maintenance gets more expensive and more difficult, readiness suffers, and more money is siphoned from future modernization to pay for current readiness," McCain said.