Inspiration from animal function can lead to effective design of engineered systems. Ocean systems benefit especially as operation in a heavy medium such as water imparts significant forces. We provide two examples of biomimetic design. In the first example, morphing fins inspired from tunas are used to dynamically change the directional stability qualities of rigid hull vehicles, enabling ultra-rapid maneuvering when deployed, while ensuring stable locomotion when retracted. Morpheus, a one-meter-long autonomous vehicle, developed with Lockheed Martin Corp. funding, demonstrated the maneuvering performance enhancement in the field. In the second example, sensors inspired from the vibrissae of sea lions exhibit great sensitivity to even minute turbulent flows, enabling the detection of plumes and underwater navigation in cluttered environments. Finally, we discuss how Machine Learning applied to experimental testing adds a new capability to underwater robotic system development.