This submarine test run went swimmingly — for a dolphin that hitched a ride on the massive Navy vessel’s surf.

America’s new Virginia-class attack sub — which is nuclear-powered for deep-ocean warfare — successfully completed its first round of “sea trials,” according to the military shipmaking firm Huntington Ingalls Industries.

Crews recording the USS John Warner’s trial last week off the Virginia coast shot a video of the dolphin tagging along on the sub’s bow wave.

The vessel submerged for the first time and passed all “components and compartments” tests, officials said.