Don't worry folks, we're not under attack. At least not directly. This epic explosion near U.S.N.'s newest combat ship is part of FSST (Full Ship Shock Trials.)
Most new Navy vessels need to take part in these trials in order to become fully operational. The idea behind these massive explosions is to "validate the operational survivability" of the ships in case of a near underwater explosion according to the Navy. With 10,000 lbs. exploding within 100 yards of the ship, you can only imagine what toll that could take on the hull of the ship.
Navy officials also stated that USS Jackson passed the trials with flying colors. Surviving a total of three such explosions off the coast of Florida, the hull of the ship sustained minimal damage. As per procedure, no crew were present on the ship.