The U.S. military’s cost estimate to build a pier off Gaza to deliver humanitarian aid has risen to $320 million, a U.S. defense official and a source familiar with the matter told Reuters.

The figure, which has not been previously reported, illustrates the massive scale of a construction effort that the Pentagon has said involves about 1,000 U.S. service members, mostly from the Army and Navy.

Still, the cost has roughly doubled from initial estimates earlier this year, according to a person familiar with the matter.

“The cost has not just risen. It has exploded,” Senator Roger Wicker, the top Republican on the Democratic-led Senate Armed Services Committee, told Reuters, when asked about the costs.