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In February 1943 Rear Admiral Mito issues SubRon 1 Secret Order No. 1 that orders Japanese submarine I-6 under the command of Monshiro Izutsu to travel to Brisbane, and lay magnetic mines in the entrance to the port of Brisbane. Izutsu was then to carry out "communications destruction warfare" in that general area until returning to Truk in late March 1943.

At 1600 hours on 2 March 1943 Japanese Submarine I-6, left Truk headed for Brisbane on her 5th war patrol where it was ordered to lay 9 German TMC type magnetic mines, near the approaches to the port of Brisbane.

On 8 March 1943 Fleet Radio Unit Melbourne (FRUMEL) decodes a Japanese message about the departure of submarine I-6 from Truk.

By about 1200 hours on 11 March 1943, Japanese submarine I-6 arrived at a location approximately 60 miles NE of Brisbane. At 1715 hours Izutsu sighted a 10,000-ton merchant and fired two torpedoes at 1844 hours. Both torpedoes missed.

On 12 March 1943, submarine I-6 reconnoiters the Moreton Bay and Caloundra Heads area and the shipping approaches to the port of Brisbane.

At 1200 hours on 13 March 1943, Japanese submarine I-6 was located approximately 12 miles off the coast just south of Point Cartwright Headland near Mooloolaba.

Submarine I-6 then moved closer to the coast and between 1850 hours and 1914 hours on 13 March 1943 laid all 9 German mines at a location within 6 miles of the coast slightly south of Point Cartwright Headland and north east of Caloundra. The mines were laid at a depth of 24 to 34 metres. Submarine I-6 then headed back out to sea.

Submarine I-6 then patrolled the area between Stradbroke Island and Fraser Island from the 14 March to the 16 March 1943.

US Naval Intelligence listening stations monitored I-6's radio transmissions. USS Stingray (SS-186), USS Trigger (SS-237) and USS Halibut (SS-232) attempted to unsuccessfully to intercept I-6.

At 1430 hours on 17 March 1943, Izutsu sights the two-ship convoy B.T.44 escorted by HMAS Gympie at a location south east of Sandy Cape.

Izutsu fired two Type 89 torpedoes at the American merchant Charles C. Jones at 1507 hours. Two torpedo wakes were spotted within 20 yards astern of the Charles C. Jones which then opens fire with its deck guns along with the guns on the ship Joseph Holt to raise the alarm with their escort HMAS Gympie.

An Avro Anson piloted by Sergeant Ron N. Walesby of 71 Squadron RAAF was on an anti-submarine patrol over the convoy at the time and managed to spot the torpedo wakes and dropped a sea marker at the assumed location of the submarine I-6. HMAS Gympie and Ron Walesby in the Avro Anson commenced a search, which lasted until 1530 hours. Sgt. Ron N. Walesby dropped a depth charge on a possible target at 1532 hours without success.

Later that night at 2022 hours, Izutsu sends a situation report (Secret Message No. 171832) to Truk. This message is partially intercepted by FRUMEL in Melbourne. As a result of the intercept, two US Naval patrol craft were dispatched to the presumed location of I-6. They were unable to locate the Japanese submarine.

Japanese submarine I-6 continued to operate in the general area and was located off Cape Byron on 21 March 1943. Izutsu received orders that day to return to Rabual where it arrived on 27 March 1943.

German mines were found washed up on Sunshine Beach, on the Sunshine Coast during WWII and another was washed up on Surfers Paradise Beach, in March 1966. Can anyone confirm whether they were linked to the mining operations of Japanese submarine I-6.

The US Navy had a large Submarine Base at Capricorn Wharf at New Farm in Brisbane. The mines that were laid by Japanese submarine I-6 were first found by HMAS Swan on 24 March 1943 when two of the mines self-detonated during target practice in that area. The area was then repeatedly swept by mine sweepers through to September 1943. As a result they discovered only one more mine.



On 11 January 1942 Japanese Submarine I-121 was in the shallow waters of Joseph Bonaparte Gulf about 125 miles south west of Darwin. I-121 laid 39 mines in the area on 12 January 1942.



On about 15 January 1942, Japanese submarine I-122 laid 30 mines in the western approaches to Torres Strait.



Japanese Submarine I-123 laid 30 mines in Dundas Strait off Cape Don on the Coburg Peninsula.



Japanese submarine I-124 laid 27 mines in the waters near Darwin in about January 1942.



Jenkins, David, "Battle Surface - Japan's Submarine War against Australia 1942 - 44", Random House Australia, 1992

IJN Submarine I-6 - Tabular Record of Movement


Australian Coastline mined during WW2
by the Allies, the Japanese and the Germans


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This page first produced 22 November 2000

This page last updated 14 January 2020