Finding the R-8 A major upgrade to side-scan sonar helps the crew of Tenacious locate a sunken World War I submarine in Northeast waters Author: Feb 5, 2021 The 186-foot-long R-8 is believed to be the last missing American sub in diveable North Atlantic waters Navsource Joseph St. Amand, sitting across from the helm aboard the 45-foot Tenacious, was the first to see the seafloor change. The images flashed on his sonar monitor for a total of 30, 40, maybe 50 seconds. He couldn’t be sure what they showed, but he knew they looked dramatically different from the previous images. “We’ve got something,” he remembers saying. “We’ve got something big.”