Japanese submarine Ro-25

The submarines of the Kaichu III sub-class were a slightly improved version of the preceding Kaichu II subclass, the man difference being an increase in diving depth from {{convert|30|to|45.7|m|ft|sp=us|0}}.Gray, Randal, ed., Conway′s All the World′s Fighting Ships 1906–1921, Annapolis, Maryland: Naval Institute Press, 1985, {{ISBN|0 87021 907 3}}, p. 248. They displaced {{Convert|740|LT|t|0|disp=flip}} surfaced and {{Convert|997|LT|t|0|disp=flip}} submerged. The submarines were {{convert|70.10|m|ftin|sp=us}} long and had a beam of {{convert|6.12|m|ftin|sp=us}} and a draft of {{convert|3.70|m|ftin|sp=us}}.

For surface running, the submarines were powered by two {{convert|1,450|bhp|lk=in|0|adj=on}} Sulzer Mark II diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a {{convert|600|hp|0|adj=on}} electric motor. They could reach {{convert|16.5|kn|lk=in|0}} on the surface and {{convert|8.5|kn}} underwater. On the surface, they had a range of {{convert|6,000|nmi|lk=in}} at {{convert|10|kn}}; submerged, they had a range of {{convert|85|nmi|abbr=on}} at {{convert|4|kn}}.

The submarines were armed with six {{convert|450|mm|in|0|abbr=on|sp=us}} torpedo tubes, four internal tubes in the bow and two external tubes mounted on the upper deck, and carried a total of ten Type 44 torpedoes. They were also armed with a single 8 cm/40 3rd Year Type naval gun deck gun mounted aft of the conning tower.

Ro-25 was laid down as Submarine No. 43 on 19 February 1920 by the Sasebo Naval Arsenal at Sasebo, Japan.{{cite web |url= http://www.ijnsubsite.info/RO-Sub%20Details/RO-25.htm |archive-url= https://web.archive.org/web/20170301090922/http://ijnsubsite.info/RO-Sub%20Details/RO-25.htm |url-status= usurped |archive-date= March 1, 2017 |title=RO-25 ex No-43 |work=iijnsubsite.info |year=2018|access-date=14 October 2020}} Launched on 17 July 1920, she was completed and commissioned on 25 October 1921.

Upon commissioning, Submarine No. 43 was attached to the Sasebo Naval District, to which she remained attached throughout her career. On 15 December 1921, she was assigned to Submarine Division 22 and to the Mako Defense Division at Mako in the Pescadores Islands. On 1 December 1922, Submarine Division 22 was reassigned to the Sasebo Defense Division.

On 19 March 1924, Submarine No. 43 was taking part in maneuvers off the harbor at Sasebo when she collided with the light cruiser {{ship|Japanese cruiser|Tatsuta|1918|2}}.[https://books.google.com/books?id=yPUtAAAAMAAJ&dq=%22Tatsuta%22+March+19+1924&pg=PA107 "Submarine Accidents Involving Loss of Life Since World War," Navy Appropriation Bill for 1929, Seventieth Congress of the United States, Washington, D.C.: Government Printing Office, 1928, p. 107.][https://trove.nla.gov.au/newspaper/article/20671316/1622449 Anonymous, "Sunken Submarine Towed Into Harbour," Reuters, 13 April 1924][https://www.wayfarerdaves.com/?p=2152 Krigbaum, David, "Picnic among the Pits: Tajimadake Naval Guard Station and Submarine No. 43 Memorial," Wayfarer Daves Travel and History, December 11, 2017 Accessed 14 October 2020.] Tatsuta sliced through Submarine No. 43′s conning tower, and Submarine No. 43 sank {{convert|3|nmi}} off Sasebo in {{convert|156|ft|m|sp=us|0}} of water. Using a telephone floated from the sunken submarine, a rescue party on the surface established contact with the crewmen trapped aboard her, who reported ever-deteriorating conditions before falling silent about ten hours after she sank. Submarine No. 43′s entire crew of 46 suffocated.

Submarine No. 43 was partially raised and towed to Sasebo, where she arrived on 13 April 1924 so that salvage operations could be completed in the protected waters of the harbor. She was fully refloated on 25 April 1924 and on 26 April was decommissioned and placed in reserve in the Sasebo Naval District to undergo repairs. While under repair, she was renamed Ro-25 on 1 November 1924. Her repairs were completed on 4 May 1925, and on 1 March 1926 she was recommissioned and returned to service in both Submarine Division 22 and the Sasebo Defense Division. On 1 December 1927 she was reassigned directly to the Sasebo Naval District and subsequently was used for trials.

Ro-25 was stricken from the Navy list on 1 April 1936. She subsequently was scrapped during 1936.

The Submarine No. 43 Memorial, a gray obelisk commemorating the 1924 sinking of Submarine No. 43, stands on Udogoe, overlooking Sasebo. It provides a vantage point from which visitors can see the area in which she sank.

{{Reflist|30em}}

• {{cite web |url=http://rekigun.net/ |title=Rekishi Gunzō}}, History of Pacific War Vol.17 I-Gō Submarines, Gakken (Japan), January 1998, {{ISBN|4-05-601767-0}}
• Rekishi Gunzō, History of Pacific War Extra, "Perfect guide, The submarines of the Imperial Japanese Forces", Gakken (Japan), March 2005, {{ISBN|4-05-603890-2}}
• The Maru Special, Japanese Naval Vessels No.43 Japanese Submarines III, Ushio Shobō (Japan), September 1980, Book code 68343-44
• The Maru Special, Japanese Naval Vessels No.132 Japanese Submarines I "Revised edition", Ushio Shobō (Japan), February 1988, Book code 68344-36
• The Maru Special, Japanese Naval Vessels No.133 Japanese Submarines II "Revised edition", Ushio Shobō (Japan), March 1988, Book code 68344-37
• The Maru Special, Japanese Naval Vessels No.135 Japanese Submarines IV, Ushio Shobō (Japan), May 1988, Book code 68344-39

• [https://www.wayfarerdaves.com/?p=2152 Photo of Submarine No. 43 Memorial at Wayfarer Daves Travel and History]

{{Kaichū type submarine}}

{{1924 shipwrecks}}

{{DEFAULTSORT:Ro-025}}

Category:Ro-16-class submarines

Category:Kaichū type submarines

Category:Ships built by Sasebo Naval Arsenal

Category:1920 ships

Category:Maritime incidents in 1924

Category:Shipwrecks of Japan

Category:Submarines sunk in collisions

Category:Warships lost with all hands

Category:Japanese submarines lost with all hands

Category:Japanese submarine accidents