The US military is mighty but needs more US-flagged ships to get its armaments overseas in times of international conflict, according to a high-ranking maritime official.

US Department of Transportation maritime administrator Mark Buzby said as the keynote speaker for Capital Link's Maritime Forum in New York.

"The commercial fleet is not where it needs to be," he said.

Of the world's large merchant ships, only 82 carry the US flag, he said.

"That puts us at No. 22 in the world," he said.

"Plain and simple, I need more ships and I need more mariners to sail them."

The US government gives 60 of those ships an annual $5m stipend to remain US-flagged, he said.

"I remind my friends in Washington — and I use that term loosely — that it is a challenge to remain under the US flag when the annual cost differential for operating a US-flagged ship and a ship under a flag of convenience is about $6.5m per year," he said.

"We need a level playing field for our ships to compete."

He said the US Jones Act is vital to US security and "fundamental corner policy" to US maritime policy.

"I need the mariners that serve on those Jones Act ships to support our sealift operations," he said.

And the smaller ships that support the larger ships employ about 41,000 workers.

"It's a jobs machine," he said.