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Anti Invasion Plans Back to Fortress Canterbury

I--- Fortifications
                  I--- Anti Invasion Plans  
                    I--- ** Banks Peninsula  **

Banks Peninsula

                                 (Click for Larger Image)

Updated 20 March 2010


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In mid 1942 Brigadier SD Mason, Commander of the Third Infantry Brigade Group was tasked by the General Staff to produce an "Appreciation of the Situation", or Battle Plan for the Defence of Banks Peninsula. 

The Third Brigade was a made up from four Territorial Force Battalions.
The CYC (Canterbury Yeomanry Cavalry, Mounted Rifles)
1st Otago battalion,
1st Southland Battalion and the
1st Canterbury Battalion,
supported by the 3rd Field Regiment, NZ Artillery.

The Brigade also had Home Guard units under its command, In this case,
The 5th Home Guard Battalion and the 8th Independent Mounted Rifles Company.    

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"Anti Invasion" Plan


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7 Pages


Brig. Mason's
"Appreciation of the Situation"

Battle Map

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Large File

A reconstruction of the map that was part of
Brig. Mason's Plan

Akaroa Harbour Minefield

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Tikao Bay Mine Depot


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The Wainui Coastal Defence Battery
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...The Akaroa Harbour Minefield
The Mine field,
An Explaination

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The Mines,
Images & Specifications
Te Kao Bay
Mine Depot
The Wainui Battery

Defensive Minefields in  Lyttleton and Akaroa Harbours


Prior to the outbreak of war with Japan, planning for the mining of major ports and harbours was well underway by October 1941.  But if General Williams' requirements were to be met, (The Defencive Plan for New Zealand) a controlled mining organisation would have to be set up. This involved the provision of suitable minelaying vessels, a mine depot, a controlled mine base to assemble the mines and their associated gear, advance bases for prepared material in the vicinity of the minefield, adequate mining material and properly trained personnel.

HMS Atreus and HMS Alsey were to lay eight minefields from Whangaroa in the north to Akaroa in the south. £69,000 was allocated for the Lyttelton & Akaroa minefields. HMS Atreus and HMS Alsey left Auckland for the South Island on 5 January 1943. The Akaroa Minefield consisted of four mine loops (each of 16 mines) and two guard loops. The field was codenamed JL8.

Note: The Atreus was a converted merchant steamer of 6546 tons gross register, built in 1911 for the China Mutual Steam Navigation Co. (Alfred Holt & Co.) of Liverpool. The Alsey was a converted trawler of 416 tons, built in 1932

After several sites in Lyttelton harbour had been rejected, Tikao Bay in Akaroa harbour was selected for the advanced base for the Lyttelton area. The Naval Board then decided upon a fully equipped base similar to that at Islington Bay and, a month later, in accordance with a policy of wide dispersion of ammunition reserves, to build eleven magazines at Tikao Bay. The estimated cost of these proposals was £97,440, as against £25,000 for the original base scheme. Authority for the additional expenditure was given by War Cabinet at the end of June 1942. But, following a visit to Tikao Bay in September 1942, the Superintending Armament Supply Officer informed the Naval Secretary that the magazine site was too far by road or sea from Lyttelton, the port to be served. Moreover, the magazines as planned would be only 200 or 300 yards away from the mining depot, with no natural feature to protect the one in the event of an explosion in the other.
On completion in 1943 it comprised of a large wooden depot of 24,500 sq ft (2275m2), a brick mine magazine, examination room and primer magazine. Land was reclaimed and a wharf built for mine laying vessels.

When they arrived at Akaroa it was found that little progress had been made with the shore buildings. Temporary huts were set up and the laying of the minefield was completed by 15 January 1943. A few days earlier, Captain Campbell of the Atreus was informed by the Naval Board that, because of the change in the strategic situation’, the Lyttelton minefield was not to be laid.

They also trained as many New Zealand officers and ratings as possible so that the efficient operation and maintenance of the controlled minefields would be assured after their departure. Yet, even before the ships had left New Zealand, the first moves were being made in a reduction programme that was to lead to the closing down of the first minefields only eleven months after they had been laid.

 It was eventually decided to build the magazines at Cass Bay, about two and a half miles from Lyttelton.

The Tikao Bay mining base was not completed till March 1943. It was then manned by an officer and fourteen ratings, all specialists on loan from the Royal Navy.

Since a big reduction in the controlled mining organisation was made shortly afterwards, Tikao Bay proved to be a white elephant of even greater proportions than the Mahanga Bay depot at Wellington.



Doubtless, in 1942,  at that time the Government had felt bound to act on the advice of their military adviser, General Williams, regarding the defence of New Zealand against a possible Japanese invasion, which to many appeared a near probability in the black months following Pearl Harbour. But, though it could not be known at the time, Japanese sources have since revealed that no attack on New Zealand was ever planned.
In respect of the minefields, it was agreed that the independent minefields in Hauraki Gulf should remain at present, except those in the channels on either side of Rakino Island, which were to be swept. The controlled minefield in Whangaparaoa Passage was to be reduced to a care and maintenance basis and that at Wellington to remain fully manned, the position in respect of both to be reviewed early in 1944. In January 1944 it was decided to dispose of all the minefields except that at Wellington. The independent minefield at the Bay of Islands was to be swept and the controlled fields there and at Whangaroa, Great Barrier, and Akaroa to be fired.  The minefield was fired on 21st February 1944.
Note: Two of the 69 mines laid in the Akaroa field are still unaccounted for and may still be resting on the floor of Akaroa harbour.  Floating mines were still being washed ashore along the New Zealand coastline as late as 1951. In all 1391 mines were laid around the New Zealand coast by the Allies and 248 enemy mines  by German raiders.

All stores were to be transferred to Islington Bay and Tikao Bay base was to be closed down and offered to the Army.

The Royal New Zealand Navy , Waters, S. D.  Historical Publications Branch, 1956, Wellington, Part of:
The Official History of New Zealand in the Second World War 1939–1945

Defending New Zealand, Ramparts on the Sea 1840-1950s, Part 2, Peter Cooke, August 2000
ISBN 0-473-06833-8

Photos: Phil Moore,

The Mines

The Akaroa Harbour Mine Field was a controlled mine field and consisted of 69 British L MkII Acoustic mines laid in 4 loops each of 16 mines and two outer guard loops, one of four and one of five mines.
The Mining Control Station was situated at Cape Three Thumbs at Wainui.


This mine can be seen at TS Cornwall, Redcliffs, Christchurch
British L Mk. II influence mine of the type laid in
Akaroa harbour.

Type L Mark II
The first reliable British contact-type mine, this was copied from the successful German Hertz-horn contact mine.  Production started in early 1917, but it was not available in useful numbers until November 1917.  Spherical design.  Total weight not available, charge was 320 lbs. (145 kg) and used Hertz horns.  Still in use during the early years of World War II.

British Mk.XVII influence mine
of the type laid in around the Northern Coast and ports.


This is an acoustic-type mine with a diameter of 40 inches, a length of 56 inches with an 8 inch belly band, a weight of 562 pounds (without sinker), and an explosive of 320 to 500 pounds.



Tikao Bay Mine Depot

(Click Image to Download as a .pdf)

(Click Plan to Download as a .pdf)
Tikao Bay Mine Depot 2009
Tikao Bay Mine Depot Workshop & Store Building Building Interior
Mine Assembly and Examination Magazine Mine Storage Magazine Primer Magazine

The Wainui Battery
The Battery Plan
(Click Here to Download as a .pdf)

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The Early Battery
"D" Sect 84 Heavy Battery
Jan 1942 - June 1943
Jan 1943 - Oct 1943
143 Heavy Battery NZA
The Battery 2009
Battery Arc of Fire
The Early Battery "D" Sect 84 Heavy Battery
Jan 1942 - June 1943
NZ 6" Howitzer of the type of gun first established at Wainui 60 lb MkI gun of the type placed at Wainui
143 Heavy Battery NZA
Jan 1943 - October 1943
No 2 Gun Colchester type Shelter A painting of a 6" MkVII gun in action, WWII
MkVII 6" Coastal Guns of the type mounted at Wainui

40mm Bofors Light Anti Aircraft Gun. Four allocated to 143 Hvy Bty for air defence 1942 (Reduced to two in 1943)

143 Hvy Battery 2009

No 2 Gun Colchester type Shelter No 1Gun Colchester type Shelter
Front of Battery Observation Post, Now converted to a Batch Looking down from Gun Position at BOP
Right of Arc, Minefield and Akaroa Heads

Defending New Zealand, Ramparts of the Sea 1840-1950's Part. 2. Peter Cooke ISBN 0-473-06833-8 2000
Archives New Zealand Christchurch & Wellington

Please treat all land that these sites are on as "Private Property" and obtain landowners permission prior to visiting.

This web page is a Draft and contains errors. Overall the information is correct but the errors refer in the most part to detail. The references that I have used to produce this presentation is conflicting. Unit numbers, place names and even the interpretation of the data conflicts with map interpretation. I have published this in its Draft form because of commitments I made from a display I did for the Arms and Miliataria show, July 2009.  I will be reviewing all the data and updating the information as I do it.

Fortress Canterbury South Island Defence 1890's - WWII - Post WWII
Coastal Defence Anti Aircraft Defence Anti Invasion  Plans NZ Military History ...
Navy Defence Installations
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Last modified: 02/10/10.