During a U.S. naval test off the California coast last month, which was designed to showcase the Pentagon’s top autonomous drone boats, one vessel stalled unexpectedly.

As officials scrambled to fix a software glitch, another drone vessel smashed into the idling boat’s starboard side, vaulted over the deck, and crashed back into the water — an incident captured in videos.

The previously unreported episode, which involved two vessels built by U.S. defense tech rivals Saronic and BlackSea Technologies, is one of a series of recent setbacks in the Pentagon’s push to build a fleet of autonomous vessels, according to a dozen people familiar with the program.