An important, and exciting, part of exploration is investigating sonar anomalies – we are never certain what will be found! Sometimes these anomalies reveal rocks, other times they show us a glimpse into our cultural heritage by revealing wreckage from years before. The “Caiman” anomaly was identified in multibeam data from early in the Deep-Sea Symphony expedition. The objective for this dive was to complete a characterization of the sonar anomaly and – if the anomaly was a cultural heritage target – confirm its identity, record its condition, and document damage from its disposal or sinking. It was thought that the anomaly could be the remains of a Japanese fast submarine I-203 (Sentaka-type) that was captured at the end of World War II and brought to Pearl Harbor as part of a five-submarine prize fleet. These submarines had been disposed of near this area in 1946, so it was certainly possible. Five waypoints were selected from the multibeam sonar targets. However, when all five waypoints were examined by the remotely operated vehicle, they were found instead to be geologic formations of basalt rock. The I-203 Japanese fast submarine was not located. There was an unexpected target identified: the remains of a World War II-period floating causeway, otherwise known as a “rhino barge.” Some of the biology highlights included a large conger eel, cusk eel, anglerfish, scorpionfish, rattail, a six-gilled stingray, crab, sea star, crinoids, urchin, bivalves, anemone, precious coral, cup coral, stony coral, jellyfish, and glass sponges.