RAN Minelaying Effort during WW2
- March 2005
- Calder, Commander Norman OBE, RAN
- History - WW2, RAN operations, Ship histories and stories, WWII operations
- DOTM, HMAS Bungaree, minelaying
- Originally published in the Naval Historical Review (all rights reserved)
This extract is taken from NHSA Monograph No. 179 ‘HMAS Bungaree – Australia’s only Minelayer’ – which was published in 2003, but has not been widely circulated.
The Admiralty suggested the manufacture of mines in Australia from 1923 onwards, but as late as December 1937 this was not considered possible by the Naval Board. As the result of further requests from the Admiralty, in 1938 negotiations were entered into with the Ford Manufacturing Company, to manufacture complete units, sinkers and mine shells. An agreement was signed in October 1939 and an order placed for 500 units (Mk XIV or XV). In April 1940 the Admiralty placed an order for a further 500 units, and it was decided to prepare plans for normal defensive minefields to meet a possible Eastern war. The requisition of a 3000 ton ship for conversion to a minelayer was also approved. The war situation was deteriorating, and in 1941 the Admiralty ordered an additional 2500 mines. It was at that time that the Naval Board decided to lay defensive minefields, the first to be at Port Moresby.
SS Bungaree was taken over by the RAN on 10 October 1940 for conversion to a minelayer at Garden Island. I was appointed (presumably to Penguin) to stand by Bungaree during conversion and in command on commissioning on 9 June 1941. I was a former torpedo specialist, and mines, as well as torpedoes, were included in this specialisation. We were also considered to be the electrical experts in a ship, but since the electrical equipment in those days was, with a few exceptions (e.g. wireless), direct current (DC), we managed to get by. The engineering branch was always sceptical of our so-called expertise in matters electrical and eventually, and particularly after AC current began to take over, they assumed responsibility.
Although Bungaree was under the Naval Officer-in-Charge, Sydney, for administrative purposes, she was under the operational control of the Naval Board in Melbourne and I had more or less a free hand. Thus I made frequent visits to Navy Office for discussions with Naval Staff and with the Director of Ordnance, Torpedoes and Mines (DOTM) as he was then called. DOTM was Captain Spooner, an ex-RN gunnery officer, who had come to Australia before the war. When it was decided to manufacture naval ammunition in Australia before the war, he was given the job of getting things underway.
The Admiralty had been loath for this to be undertaken outside the UK. Such was the strict inspection required at definite intervals for explosives that outfits of ammunition were stored in naval armaments depots around the world, where ships could exchange their outfits when circumstances demanded it. The Admiralty were not keen to have Australian-made ammunition absorbed into their stocks; however, they agreed reluctantly, provided that all ammunition was manufactured strictly to Admiralty drawings and specifications, and subject to strict naval inspection. This necessitated the creation of an Australian Naval Inspection Branch with an Inspector of Naval Ordnance. He had a dual responsibility: first to organise the manufacture and supply of ammunition to the Fleet, and then to inspect it before it got to the Fleet. This was an anomalous situation, for it was a conflict of interests: one is not generally allowed to inspect one’s own work for compliance with the regulations. In the RN, supply to the Fleet was in the hands of civilians and was quite separate from the Inspection Branch (as it should have been regarding separation of responsibilities).
Captain Spooner (DOTM) was given the job of producing the mines, sinkers and explosives for the mines and so was high on my visiting list, as the planning of the defensive minelaying depended upon the supply of mines being available. When I first called at Navy Office I found that their knowledge of minelaying was minimal. The staff could appreciate the general situation and their strategy for the placement of defensive minefields, but it ended there. Whether their plans were practicable or worthwhile, this decision more or less devolved on me. I had no previous experience in minelaying, except during my long course in HMS Vernon, and had no idea of the suitability or otherwise of Bungaree for the job.
Time and Experience
Time and experience would be needed to ascertain whether a minefield was worthwhile from the physical deterrent angle (quite separate from the strategic value) and primarily involved a consideration of probabilities. I had a bit of a reputation as somewhat of a gambler, inclined to bet on anything, and hence had some practical knowledge of the meaning of the word ‘probability’. The staff told me that the first defensive minefield was to be laid in the approaches to the harbour of Port Moresby on either side of the main entrance, named Basilisk Passage, and inside the reef which stretches along the coast of Papua. Basilisk Passage itself was not to be mined. The minefield was to be anti-submarine. I was more or less told to get on with the job of planning the minefields.
There were two sizes of explosive charge that could be used in the mines, either a 500lb charge of TNT or one of 320lb. The larger would be classed as anti large surface ship and the smaller anti-submarine. The larger charge naturally had a greater damage radius than the smaller. They were contact mines (i.e. there had to be physical contact between target and mine). The depth of the mine below the surface could be adjusted. There was a maximum depth at which the mines could be laid but it was sufficient to cope with the areas in which the mines were to be laid. There was also a minimum distance between adjacent mines to prevent sympathetic counter-mining (i.e. one explosion setting off adjacent mines in the minefield).
One had to assume certain parameters such as the dimensions of the target and, in the case of submarines, the various depths at which they might be operating when approaching the minefield. The capacity of the minelayer (423 mines) had to be considered, and the manoeuvrability of the ship to mine amongst reef areas (in some cases only lightly surveyed) had to be determined by turning trials. Knowledge of the weather pattern of an area was most desirable, especially after speed and turning trials of Bungaree showed that good weather conditions at the time of laying were highly desirable, if not essential.
There was a publication called the ‘Mining Manual‘ compiled in HMS Vernon but I do not remember getting much data on the planning of minefields from it. After my first efforts in planning I decided to approach the mathematicians. I got in touch with Sydney University, explained the situation as best I could and asked for guidance, particularly as regards probability and the best pattern to use. I had hoped to be given an equation or formula, a child’s guide where one just had to accept figures for symbols, and presto, we had the best pattern to use and the probability of success. What I got back was a tome, about half an inch thick, which after reading made my confusion worse confounded! It was a grand effort on the part of the University and much appreciated, but it was a mass of equations and figures too abstruse for the simple sailor. I tried it out on other people but received no enlightenment, so I knew it had to be me, to go about it to the best of my ability. This used up a lot of graph paper, drawing rows of mines at various depths and spacing. I must have reached some answers but in many cases it was hit or miss.
Meanwhile, the conversion at Garden Island Dockyard proceeded. Garden Island was pretty busy at the time but I cannot remember being frustrated by delays. Bungaree was a shelter deck ship; that is, the deck below the upper deck ran more or less continuously from forward to aft and from which you descended into the holds. The requirement was to clear away those obstructions, which would then enable rails to be welded to the shelter deck and permit the mines to be lowered onto them.
Two holes had to be cut in the ship’s stern for the mine chutes (through which the mines dropped into the sea astern). The mines were hauled aft along the rails by winches at the forward end of the shelter deck, by means of wire ropes attached to what were called ‘bogies’ situated behind the lines of mines. There were four sets of rails, two either side of the shelter deck, but only two stern discharge ports, fitted with traps. The mines were hauled aft by the winches into the traps, which were hand operated to allow the mines to pass through them into the sea. Hand operated ‘points’ were fitted near the traps allowing mines from either rail each side to enter the traps. There were continuous lengths of stout wires running from the winches through rigging blocks to the bogies, to haul the mines aft into the traps. There were necessary comm- unications from the bridge to the mining deck (e.g. time interval clocks, telephones etc.) and the mining deck (as it was called) was well lit. The whole deck could be compared to a railway shunting yard and one had to watch one’s step to prevent tripping over wires and rails. Once mining operations started the noise level was pretty high, necessitating plenty of preliminary drills on the mining deck. I think there was a slight dip between the winches and the traps necessitating the wires being kept at the same height as the rails by means of wire guards. The noise level once the row of mines started to move aft was a bit nerve racking and required good drill and individual initiatives when ‘hang ups’ looked like happening. I have used the term ‘mine‘ when mine unit would be more precise.
A mine unit comprised a mine shell containing an explosive charge case (500lb or 320lb TNT), to be fitted with a primer and detonator in the charge, connected to an electrical battery through an external ‘horn’, which was broken or actuated by contact with the hull of a ship or submarine, thus exploding the mine. They were known as contact mines. The mine shell was affixed to a sinker by clamps. The sinkers were large rectangular boxes with four small wheels at each bottom corner. These fitted inside the rails so that the mine unit could roll along them when hauled aft by the winches. Inside the sinker was a drum of mooring wire, one end of which was attached to the mine case. There was also a depth mechanism, which enabled the distance of the mine below the surface to be set to any predetermined amount.
On being dropped into the sea through the traps at the end of the mine rails, the mine separated from the sinker which then sank to the bottom, dragging the mine to the set distance below the surface, having previously been set on the depth mechanism in the sinker. There was a safety device fitted which prevented the mine becoming active for a sufficient interval for the minelayer to clear the minefield. On the mining deck was a time clock, which could be set to sound at the required time interval needed between each mine being dropped. This depended upon the speed of the minelayer over the sea bottom and the distance required between each mine. All orders to the mining deck came from the ship’s bridge. I was in overall control when minelaying commenced but was assisted by the navigating officer, responsible for the required manoeuvres. At a ship’s speed of 10 knots, the average time interval between each mine lay was approximately 11 seconds. A full mining deck of 250 mine units took about 45 minutes to lay.
(The Monograph goes on to describe the other aspects of the ship, her crew, personalities, and the operations conducted throughout her busy war. This is a unique account of a most unusual and hard-working warship and is highly recommended to our readers. After the War she reverted to merchant service and ultimately met her end being mined herself off Saigon in 1966! Ed).
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