A convoy of five American cargo ships made a simulated run through hostile waters in September 2019 during a sprawling, short-notice test of the U.S. fleet’s ability to ship people and cargo during a major war.

The simulated, World War II-style convoy underscored the importance of sealift to U.S. war plans, as well as the shortage of naval escorts that has incited a minor panic among military planners.

The five ships in the East Coast convoy test included the roll-on/roll-off cargo vessels USNS Benavidez, USNS Gilliland, and USNS Mendonca, USNS Pfc. Eugene A. Obregon and USNS Sgt. Matej Kocak.

All five vessels belong to U.S. Military Sealift Command, the quasi-military transport branch of the U.S. Navy. MSC operates more than 100 vessels. Many of them lie inactive in major ports during peacetime. During a crisis, Navy and civilian mariners quickly would reactive the ships.

The September 2019 transportation “stress test”  activated a total of 33 sealift ships on both U.S. coasts. As part of the exercise, the five East Coast ro/ro ships simulated an unescorted convoy moving through waters where enemy submarines and sea mines posed a threat.

“The convoy sailed through a simulated minefield while limiting visual and sound signatures,” USNI News reported, citing an MSC statement. “Crews stopped using all personal electronic devices to decrease transmissions from the ships and operated in a ‘darken ship’ mode to prevent light from emanating from the ships.”

“We were also training the crews to sail their ships as quietly as possible to counter ships’ electromagnetic signatures because our vessels also could face anti-ship ballistic missiles, cruise missiles, fighter aircraft and enemy bombers,” Capt. Hans Lynch, MSC’s Atlantic commodore, said in the official statement.

The training belies a serious shortage of surface warships that could function as escorts. In October 2018, U.S. Maritime Administration head Mark Buzby said the Navy admitted it wouldn’t be able to escort sealift ships during a major war with Russia or China.

The Navy is struggling to expand the fleet from around 290 front-line ships in 2019 to as many as 355 in the 2030s. But the cost of building and maintaining the extra ships has cast into doubt the sailing branch’s ability to meet its expansion goal.

The Congressional Budget Office consistently has maintained that Navy shipbuilding accounts are billions of dollars too low on an annual basis in order to fund the bigger fleet.

With too few warships to escort the sealift vessels, MSC crews would be on their own. To help them survive, they should “go fast and stay quiet,” Buzby said the Navy told him.

That’s exactly what the crews of the five East Coast MSC ships did in September 2019. Between 80 percent and 85 percent of the ships in the wider shipping stress test successfully met the underway evaluation criteria, a U.S. Transportation Command spokesperson told USNI News.

But the U.S. sealift force has other problems. For one, it’s too small, the Washington, D.C. Center for Strategic and Budgetary Assessment warned in a May 2019 report.

The civilian merchant marine, which during wartime would become an auxiliary force under the Navy, possesses around 180 U.S.-flagged vessels. Add in MSC’s own ships and the overall U.S. sealift force numbers around 300 ships.

But by 2048 it needs to grow to 360 ships in order to successfully support the Navy and resupply U.S. military forces during a major war, CSBA asserted. The fleet should add 48 tankers ships to its current 21 tankers, add 20 salvage ships to the five it has in 2019 and boost the number of repair tenders from two to 17. Munitions ships should number 25, up from 12 in 2019. There should be seven hospital ships, up from two.

“Failing to remedy this situation, when adversaries have U.S. logistics networks in their crosshairs, could cause the United States to lose a war and fail its allies and partners in their hour of need,” CSBA warned.

Adding more than 60 ships to the sealift fleet is a tall order and could cost billions of dollars. But experts’ warning have not gone entirely unheeded. Kevin Tokarski, a senior official with the U.S. Maritime Administration, in May 2019 told USNI News that he was considering reflagging some ships working for American companies in order quickly to grow the sealift force.

David Axe serves as Defense Editor of the National Interest. He is the author of the graphic novels  War Fix, War Is Boring and Machete Squad.