The U.S. Navy's efforts to build a fleet of unmanned vessels are faltering because the Pentagon remains wedded to big shipbuilding projects, according to some officials and company executives, exposing a weakness as sea drones reshape naval warfare. The lethal effectiveness of sea drones has been demonstrated in the Black Sea where Ukraine has deployed remote-controlled speed boats packed with explosives to sink Russian frigates and minesweepers since late 2022. These tactics have caught the attention of the Pentagon, which is incorporating lessons from Ukraine and the Red Sea into its plans to counter China's rising naval power in the Pacific, Pentagon Spokesman Eric Pahon told Reuters.