IJN Submarine I-12

Date of Action: 13 November 1944

USCG Units Involved: USS Rockford, PF-48, a Coast Guard-manned frigate [in concert with US Navy's USS Ardent, AM-340.]

Sinking/Capture/Assist? Probable sinking, credit shared between Rockford and Ardent.

Location: 31'- 55" N x 139' - 45" W 

Credit by U.S. Navy? Yes, probable sinking (see below).

Enemy warship's commanding officer: CDR Kudo Kaneo

Enemy casualties: 114

U.S.C.G. casualties: None


The USS Ardent (AM-340) and the Coast Guard-manned frigate USS Rockford (PF-48) escorted a six-ship convoy from Honolulu to the United States' mainland in November 1944.  As they approached the midway point of the voyage, the Ardent made a sonar contact ahead of the convoy.  She began plotting the contact and made two hedgehog attacks with negative results.  The Rockford then made a "well conducted attack" with a 13-charge hedgehog pattern.  Fifteen seconds later the crew heard three distinct hedgehog detonations and four minutes later they heard numerous underwater explosions.  Water and air bubbles were then observed "boiling" on the surface, along with diesel fuel and debris, including teak deck planks (one with Japanese builders' inscriptions), ground cork, pieces of a vegetable crate covered with labeling in Japanese, pieces of varnished mahogany with tongued and grooved material, and one piece of smoothly finished wood from instrument case, with loose screws around the edges, and inscribed with Japanese writing.  

The subsequent analysis concurred that three hedgehog charges detonated against the submarine, causing its destruction.  Both warships were given equal credit in the probable destruction of a Japanese submarine.  The only Japanese submarine operating along the west coast of the United States at that time was the I-12, which had attacked and sank the SS John A. Johnson on 30 October.  

Technically their claim remains unconfirmed as the sinking was not corroborated by Japanese documentation captured after the war.  Japanese sources indicate that the submarine was active through December and is listed as having been lost in January, 1945 from unknown causes.  Nevertheless, due to the clear sonar contact, the accuracy of the attack including three hedgehog explosions, and the debris recovered, it is most probable that the Rockford and the Ardent did, in fact, sink the I-12.


Memo, COMINCH, United States Fleet, Incident No. 7282, "Analysis of Anti-Submarine Action By USS Rockford (PF-48) and USS Ardent (AM-340)." 

W. J. Holmes.  Undersea Victory: The Influence of Submarine Operations on the War in the Pacific.  Garden City, NY: Doubleday & Company, Inc., 1966, p. 413.

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Last Modified 1/26/2012