The Pentagon has expanded its use of maritime shipping to deliver weapons for the war in Ukraine, U.S. defense officials said, after relying heavily on aircraft early in Russia’s invasion to get arms to Kyiv as quickly as possible, The Washington Post reported.

The Defense Department began sending some items by sea a few weeks after the invasion but significantly broadened the effort this spring, as the United States began providing Ukraine with howitzer artillery and other heavy weapons that require a steady flow of large-caliber ammunition, U.S. defense officials said at the headquarters of U.S. Transportation Command, as Deputy Defense Secretary Kathleen Hicks visited recently.

“Once we started to provide them howitzers, we knew that we were going to need more ammunition,” said Army Col. Steven Putthoff, the deputy director of operations at U.S.

Transportation Command. “So, we could plan ahead a little bit more, and then we could start to use more sealift to provide that support and to get it there sometimes even ahead of the request.”