During 1943 to 1945 - what would become the latter half of World War (1939-1945) - the Imperial Japanese Navy (IJN) put effort into construction of six projected, special-purpose "tanker/resupply" submarines as the I351-class. Born from a 1942 initiative, the class was led by I-351 herself, becoming the only completed vessel of the group before the end of the war in August 1945. A second vessel was destroyed while under construction while four of the group were cancelled outright when the need for such specialized boats was no more - by this time the IJN had lost more of its important forward-operating bases to the Allied advance.
As designed, the I351-class was intended to ferry up nearly 400 tons of wet or dry supplies to awaiting flying boats and floatplane aircraft operating in forward positions all over the Pacific. As a transport system, I-351 was rigged to carry fuel stores, fresh water and munitions - from conventional drop bombs to torpedoes. Beyond her hauling role, the I-351 was also outfitted for potential trouble with 4 x 533mm (21") torpedo tubes of her own though she carried only four reloads resulting in a limited offensive punch. The boat also retained useable surface armament consisting of 3 x 81mm Type 3 mortars and 7 x 25mm Type 96 Anti-Aircraft (AA) cannons.
As built, I-351 displaced at 3,570 tons when surfaced and 4,560 tons when submerged. She featured a running length of 364.1 feet with a beam of 33.5 feet and a draught of 20 feet. Power was from 2 x diesel engines outputting at 3,700 horsepower and 2 x Electric motors governed the vessel at 1,200 horsepower when submerged. Both arrangements drove 2 x shafts at the stern. Maximum speeds reached 16 knots when surfaced and 6 knots when under water. Range was an impressive 15,000 miles while the hull was tested at depths of 300 feet, comparable with submarines of the period. Her entire crew complement numbered 77 officers and enlisted with an additional thirteen men serving as part of the onboard aircrew.
I-351 became the only completed vessel of the class, launched in 1944 from the Kure Naval Arsenal shipyard. She was eventually (and officially) completed on January 28th, 1945 though her ocean-going career would last only until July 14th, 1945 when she was successfully engaged by the USS Bluefish (SS-222) submarine and sunk. Her sister, I-352, was lost in an American-led air raid a month earlier on June 22nd, 1945 while still held at the Kure Naval Arsenal. At the time of her sinking, I-352 remained nearly 90 percent complete. I-353's hull was never laid down and the remaining three, proposed boats only ever received their construction numbers as #730, #731 and #732.