If you want to build a soft-bodied robot that can swim fast, then you would do well to borrow some ideas from the design of the fastest of all aquatic invertebrates — the squid.
That was the starting point for a team of engineers at the University of California San Diego. Their robot squid is designed to explore underwater environments without harming fish and coral, as a robot with a rigid body could.
The robot carries everything it needs onboard so that it can swim without the need for a tether. For propulsion, the robot ingests water into its body, then releases elastic energy stored in the flexible body and ribs to generate a jet of water. A side effect of changing body shape is an increase in swimming efficiency. Adjusting the position of the nozzle will move the robot in any direction desired. A watertight compartment at the front can house a camera or other sensors.
At 0.5 miles per hour, this squidbot may not sound especially fast, but it can swim laps around most other soft robots.
After completing lab tests, the robot was taken to a large aquarium at the UC San Diego Birch Aquarium. There the squidbot was able to successfully maneuver around coral and fish to demonstrate its feasibility for real-world applications.