The last submarines built by our Navy to be designated by a combined letter and numeral were the S-class - the so-called S-boats. They started building them way back in 1916, and before the program was completed, 51 of these sturdy craft had slid down the ways. The Navy's later types of undersea ships were given names of fish or other aquatic dwellers. At the same time they were laying keels for the S-boats, they also built 27 R-boats, but they were relatively small, and useful mainly for coastal patrol.
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