Underwater robots have always come in two flavors. The swimmers cover long distances on battery power and take pictures, and the workers hang off a thick cable beneath a crewed ship and actually turn wrenches. You picked one, because no single machine did both jobs well. A Houston company called Nauticus Robotics builds the exception. Its Aquanaut Mk2 is a 4,200-kilogram (about 9,260-pound) electric drone, 16 feet long, that swims out to a job site like the first kind of robot, stops in open water, and puts a pair of electric arms on the problem like the second kind. The company even has names for the two personalities: excursion mode when it swims and scans, intervention mode when it goes to work. And the arm side of the business just got busy. On July 28, Nauticus announced the completed first prototype of a next-generation electric manipulator built specifically for autonomous vehicles like this one. Then on Wednesday, in its second-quarter update, the company said it is steering the whole package toward defense work. One hull, two different machines Most long-range underwater drones look like torpedoes, because a torpedo is the cheapest shape to push through water. The Aquanaut is a broad, flattened slab instead: 16 feet long, 6.7 feet wide and 5.6 feet tall (4.82 by 2.03 by 1.71 meters), with an oval ring tail carrying the two main thrusters and a set of tunnel thrusters for hovering and holding position in current. That shape exists because the machine leads a double life. In excursion configuration it carries sonar, laser scanners and cameras, and behaves like a survey drone. In intervention configuration it carries two robot arms and behaves like the tethered work vehicles the offshore industry has leaned on for decades, except nothing tethers it. It also packs a