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caisson made from carbon steel, which serves as the watertight ‘sucking’ structure. Once it has mated with the seafloor, a pumping system draws out the saltwater inside it, an altimeter provides depth information to the UUV, and an electrically actuated winch lowers the anchor by a tether. To deploy the anchor, two linear actuators open a pair of bay doors in the underbelly on the opposite side from the antenna fin, and the winch extends a tether containing a Power-over-Ethernet cable connecting the anchor and the UUV. The tether runs up from the winch and down through a pulley, which also contains a load sensor. Through that, the UUV measures the ‘pull’ on the tether, to help inform whether to command the winch to extend or reel back the line. The caisson is 50.8 cm in diameter, and its pumping system uses an electrical centrifugal pump to push water from inside the caisson into an eductor (a jet pump ejector) and then outside. The reduced internal pressure causes the anchor to ‘suck’ down and slowly push into the silt. About 300-400 W of power is typically used by the system, and is divided roughly equally between the winch and the anchor. It typically takes between six and 10 minutes to fully embed the caisson. As Cellula’s mechanical design engineer Sina Doroudgar explains, “In the beginning, we wrote a proposal for a deployed device that would secure the UUV to the seafloor to perform cone- penetration testing measurements of the silt or similar inspections of that nature. “There were a few ways we could have designed it, but in any case it gradually dawned on us and our clients that we could use this as an anchor that didn’t rely on weight or grappling hooks.” The current version of the system is the company’s Mk 2. A prototype was built in late 2018, and the engineering team carried out a range of tests using variants of the caisson to determine the optimal ratios of its height and diameter. It also investigated its holding capacity in two types of silt.