Acoastal submarine orlittoral submarine[1] is a small, maneuverablesubmarine with a shallowdraft well suited to navigating coastal channels and harbors. Although size is not precisely defined, coastal submarines are larger thanmidget submarines, but smaller than sea-going submarines designed for longer patrols on the open ocean. Space limitations aboard coastal submarines restrict fuel availability for distant travel, food availability for extended patrol duration, and number of weapons carried. Within those limitations, however, coastal submarines may be able to reach areas inaccessible to larger submarines, and be more difficult to detect.
The earliest submarines were effectively coastal submarines, but as modern submarine tactics developed duringWorld War I, the advantages of rapid construction and portability encouraged the development ofUBtorpedo launching, andUCminelaying coastal submarines in 1915 to operate in theEnglish Channel. These coastal submarines displaced only 15 to 20 percent of the weight of a contemporary conventional U-boat,[2] could be built in one-quarter of the time it took to complete a conventional U-boat, and be delivered on railway wagons to operating bases inBelgium.[3] Improved versions of UB and UC coastal submarines were devised. Total production of German coastal submarines during World War I was 136 type UB and 95 type UC.[4]
German submarine construction between the World Wars began in 1935 with the building of 24Type II coastal submarines. These coastal U-boats, with another eight completed prior to hostilities, madeNorth Sea combat patrols during the early months ofWorld War II and then served in theBaltic Sea training crews to operate ocean-going submarines.[5] The30th U-boat Flotilla of six Type II U-boats was transported overland via theAutobahn and then down theDanube for combat patrols in theBlack Sea until September 1944.[6]
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