The submarines of the K6 sub-class were versions of the preceding K5 sub-class with greater range and diving depth. They displaced 11150NaN0 surfaced and 14470NaN0 submerged. The submarines were 80.5m (264.1feet) long, had a beam of 7m (23feet) and a draft of 4.07m (13.35feet). They had a diving depth of 80m (260feet).[1]
For surface running, the boats were powered by two 21000NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor.[2] They could reach 19.75kn on the surface and underwater. On the surface, the K6s had a range of 11000nmi at ; submerged, they had a range of 45nmi at .
The boats were armed with four internal bow 53.3cm (21inches) torpedo tubes and carried a total of ten torpedoes. They were also armed with a single 76.2mm L/40 anti-aircraft gun and two single 251NaN1 AA guns.[3]
Ro-49 was laid down on 16 November 1942 by Mitsui Zosensho at Tamano, Japan, as Submarine No. 390.[4] She was named Ro-49 on 31 July 1943 and was attached provisionally to the Maizuru Naval District that day.[4] Launched on 3 August 1943,[4] she was completed and commissioned on 19 May 1944.[4]
Upon commissioning, Ro-49 was attached formally to the Maizuru Naval District and assigned to Submarine Squadron 33 for workups.[4] In mid-July 1944, she and the submarine took part in tests of a submarine version of the Type 13 air-search radar.[4] She was reassigned to Submarine Squadron 11 on 15 August 1944[4] and then to Submarine Division 34 in the 6th Fleet on 10 November 1944.[4]
On 16 November 1944, Ro-49 departed Kure, Japan, to begin her first war patrol, assigned a patrol area in the Philippine Sea east of Luzon in the Philippine Islands.[4] Her hydrophone suffered damage in rough seas, and on 28 November 1944 her commanding officer decided to return to Japan.[4] She returned to Kure on 7 December 1944.[4]
Ro-49 set out from Kure on 1 January 1945 to begin her second war patrol, again in the Philippine Sea east of the Philippines.[4] On 4 January 1945, she received new orders to patrol in the South China Sea west of Luzon.[4] U.S. forces entered Lingayen Gulf and U.S. forces began their invasion of Luzon on 9 January 1945.[4] Ro-49 was in the South China Sea west-northwest of Iba on Luzon on 12 January 1945 when she sighted two escort aircraft carriers and three battleships with a strong escort.[4] She attacked and her commanding officer reported that she sank what he described as an "Idaho-class" battleship, but her claim of hitting a battleship was disproven after World War II.[4] On 21 January 1945 he received an order to return to Kure, which she reached on 1 February 1945.[4] She moved to Saeki on 16 March 1945.[4]
On 18 March 1945, Ro-49 got underway from Saeki for her third war patrol, assigned a patrol area southeast of the Ryukyu Islands.[4] After she sent a routine situation report on 25 March 1945, the Japanese never heard from her again.[4]
On 26 March 1945, a Japanese submarine attacked United States Navy Task Group 54.3 off the Ryukyus. At 09:32, the heavy cruiser sighted a periscope to starboard, and she made an emergency turn to starboard to evade a torpedo.[4] The light cruiser also sighted torpedo wakes.[4] The attacking submarine scored no hits but escaped without facing a counterattack by the cruisers′ escorts.[4] The identity of the attacking submarine remains unknown, although historians have attributed the attack both to Ro-49 and to a Type C Kō-hyōteki-class midget submarine, in the latter case also claiming that the attack took place on 27 March 1945.[4]
On 5 April 1945, the destroyer was on radar picket duty off Kume Island near Okinawa when she received a signal from the support landing craft reporting the sighting of a submarine.[4] While the submarine was on the surface, Hudson detected it on radar at 0345.[4] Hudson closed the range and fired a star shell to illuminate the area, and the submarine dived, causing it to disappear from Hudson′s radar.[4] However, Hudson established sonar contact on the submerged submarine and made six depth-charge attacks over the next six hours, sinking the submarine at 26.3667°N 156°W.[4]
The identity of the submarine Hudson sank remains unclear. It could have been Ro-49. Some Japanese sources claim that Ro-49 was already missing by 5 April 1945 and that Hudson sank the submarine,[4] although I-56 might have been sunk on 18 April 1945 instead.[5] Some accounts claim that the submarine sank Ro-49 in the Bungo Strait on 24 February 1945, but Ro-49 was active for at least a month after that date.[4]
On 15 April 1945, the Imperial Japanese Navy declared Ro-49 to be presumed lost southeast of Okinawa with all 79 men on board.[4] She was stricken from the Navy list on 25 May 1945.[4]