Mines and Mine Laying in Iceland WWII
A HAZARDOUS LEGACY
WW II Sea Mines around Iceland
Operations by the Icelandic Coast Guard EOD (Explosive Ordnance Disposal) Unit to render safe and destroy stranded and trawled WW II Sea Mines on and around Iceland has awoken much interest on the history of these mines and the dangers they now present to both fishermen and the general public.
ICG EOD Pic 1. 227 kg Main Charge from UK Mine on Icelandic Trawler – Detonator assembly still in place.
To answer the first question we must refer back to WW I, when the British laid North Sea Mine Barrage was established between the Orkney Islands and Norwegian coast after a plan conceived by the US Navy. This mine barrage was laid in an attempt to reduce the devastating shipping losses to the allied merchant fleet by German Warships and Submarines, which in June 1917 were as high as 685.000 tons per month.
It was predicted at the time that if losses continued on the same scale, the war effort would be undermined to such an extent that the defeat of Britain would be inevitable, not by defeat of the land army in the field, but by the inability to supply the nation and its military with necessary foodstuffs and logistic support.
The North Sea barrage was eventually laid in June 1918, but its results were, proportional to the 70.000 mines laid, not spectacular, with only two possible sinkings of U-boats officially recorded. Other tactical measures such as the introduction of the convoy system, did however contribute to a substantial and telling reduction in losses to the merchant shipping fleet. With the war eventually won in November 1918; the lessons learned and experiences gained from the North Sea Mine Barrage Operation were remembered by the British Admiralty and although the results were less than impressive, the concept was to be reintroduced when tensions in Europe led to another conflict between the same antagonists in 1939.
The Northern Mine Barrage.
During WW II Winston Churchill commented that of all the threats posed to the British Nation by Germany, attacks on Merchant Shipping were the most likely to bring defeat, especially attacks made by U-Boats, which, at the beginning of the war were far in advance of Royal Navy anti-submarine countermeasures. To oppose this serious threat to Britain’s survival, plans were made in July 1939 to repeat the North Sea Barrage of WW I, in an attempt to contain or at least make difficult the passage of German raiders from their home ports into the Atlantic Ocean via the North Sea and Northern Atlantic.
The initial plans for the barrage however, had to be abandoned when Germany invaded and eventually occupied Norway in 1940. War though, being a great motivator, lead to a complete revision of the plan by the Admiralty and subsequently a modified but more expansive operation was eventually proposed and accepted. Thus was the beginning of the most ambitious mine laying operation of that time, the Northern Mine Barrage.
The laying of the Northern Mine Barrage was given the code name Operation “SN” by the Royal Navy and its objectives were set out as:
1. The prevention of enemy raiders, U-boats and U-boat minelayers from leaving the North Sea and attacking British trade routes and restricting enemy mining activity in the North Sea area.
2. Assisting Contraband control in the North Sea area.
3. Providing protection for Scandinavian Convoys.
4. Reducing the losses to capital ships through U-boat action.
In order to carry out the operation, 10 merchant ships were required; this figure was subsequently reduced to 5 vessels by special modifications to the mines, so reducing the numbers required to effectively achieve the barrage. The mine laying vessels initially commissioned after extensive modification were: HMS Southern Prince (Flag Ship) 10,917 tonnes, HMS Port Napier 9.600 tonnes, HMS Agamemnon 7.593 tonnes, HMS Menestheus 7.494 tonnes and HMS Port Quebec 5,936 tonnes. The vessels could carry between 438 and 556 mines each depending on tonnage.
HMS Port Quebec prior to modification
The mine laying vessels would be known as the First Mine Laying Squadron and as well as the Northern Barrage would have other mine laying commitments to fulfil around the British Isle, particularly on the East Coast and South Western approaches.Implementation of the plan meant a huge cost in valuable war materials such as steel; the mine manufacturing contracts were given to amongst others, the Wolsely Motor Company of Oxford, with the explosives filling of the mines to be undertaken at Bandeath near to Stirling, Scotland. An operational base was established on 17 June 1940 at Kyle of Lochalsh on Scotland’s west coast under the command of Rear Admiral W. F. Wake-Walker. In order to lay and maintain the mine fields the operation would be continuous, with fields having to be swept and re-laid at regular intervals depending on the operational life of the mine, which could vary considerably under the prevailing sea conditions found in the North Atlantic.
Being only lightly armed with a single High or Low angle 4 inch gun and a small calibre Anti-Aircraft gun, it would be necessary to escort the Mine Laying Squadron on each mission by more powerful Warships, and on most occasions, in addition to a close escort of Destroyers, the Squadron was covered by main fleet assets. Capital ships such as the illustrious but ill fated Battleship HMS Hood took part in Operation “SN” as did HMS Belfast and HMS Edinborough also of tragic fate. This was to be a major undertaking by the Royal Navy and one which, it was hoped, would both reduce merchant shipping losses and ease the mounting pressure on stretched British Naval resources, by having to patrol reduced areas of the vast North Atlantic Ocean.
The operation lasted for approximately 3 years during which time the First Mine Laying Squadron laid over 110.000 mines, the majority of which were laid between the Faeroe Islands and Iceland. Mines were also laid between the North of Scotland through the Orkney Islands to the Faeroes and from the North West of Iceland to the Greenland Ice Belt. Navigation channels were left between the fields for naval vessels and warnings to friendly mariners were given out by the Admiralty. In operations where all vessels were available for laying, over 2600 mines could be laid out in one mission, but on most occasions, whether through other commitments, damage or repair, it was uncommon for all vessels to be employed at one time.
Contact with the enemy occurred on several occasions, and in one encounter HMS Southern Prince, on her return to base from a mine laying mission, was torpedoed but not sunk by U-652; she was eventually repaired and returned to service. HMS Port Napier was lost in home port due to an accident onboard, when through reasons unknown a fire broke out causing the detonation of several mines. Just after this accident, Admiral Wake-Walker was replaced by Rear Admiral R.L. Burnett. Further accidents occurred during mine laying operations, one prevailing cause of accident was when drifting mines became entangled in the mine laying gear and subsequent detonation of the mine caused extensive damage to the vessels.
The value of any military operation can only be measured by results and on several occasions the viability and value of this great effort was both questioned by its critics and examined periodically by the Admiralty. Losses to merchant shipping were indeed eventually reduced, but not necessarily as a result of the Mine Barrage, but as a result of the technological and tactical developments in the relentless war against the U-Boat. The hunter became the hunted and lost the ascendancy, thus negating the need for the continuance of Operation “SN”. On 26 September 1943 the operation was officially ended and the First Mine Laying Squadron disbanded.
Fig 1. Operation “SN” Minefields SE of Iceland Fig 2. Operation “SN” Minefields NW of Iceland
If indeed, we measure the results critically it can be said that Operation “SN” was unsuccessful in achieving its operational objectives. The operation constituted 35% of British mining operations in WW II and far more was expected of the minefields by its designers and promoters. It did not deter raiders and U-Boat attacks, which after the conquest of France originated not necessarily from Ports in Germany and the Baltic, but from ports on Frances Western seaboard. One of the operation’s only tangible successes was the detection of the Bismarck, which, having sailed through minefield “SN 71B” in the Denmark Straight, was detected and eventually sunk with huge loss of life to both sides. The Bismarck and her escort the Scharnhorst had actually avoided detonation of the mines by sailing over the minefield at high water, which meant that there was at least 10 m of water over the mines. It was also reported that the effectiveness of this minefield had been compromised by the movement of ice. One U-boat, U.702, was confirmed as being sunk as a result of collision with a mine off the South East of Iceland, although it is possible that others may have been lost as a result of operation “SN”.
There were a number of allied tragedies as a result of the mine barrage, including the sinking of the destroyer HMS Achates with the loss of 60 lives in July 1941 and the sinking of five ships from convoy QP13 in July 1942 on its return from Murmansk to Reykjavík, after delivering valuable war materials and supplies to Russia. The convoy was lead and escorted by HMS Niger. Niger, on mistaking an iceberg for Iceland’s North Western Cape lead the convoy into minefield “SN 72” at the entrance to the Denmark Straight and although recognising his mistake, the Captain could not take avoiding action in time to save either his ship or the other unfortunates in the convoy.
In a statement summarising Operation “SN”, the Commander in Chief of the Home Fleet, Admiral Bruce Fraser, said in 1943, that the laying of the Northern Barrage had been “the least profitable voluntary major naval undertaking of the war”; one has however to balance these rather harsh words against the vast human effort and sacrifices made in the course of the operation. The laying of the fields was after all successful, and this carried out with grim determination under constant threat of attack by the enemy and in the harsh conditions found in the North Atlantic Ocean.
The Mines used in Operation SN
The mines used in Operation “SN” were of the Buoyant Anchored type, which is, simply put, an Explosive Charge Barrel, Booster/Detonator Assembly and Firing Mechanism held within a buoyant welded steel hemisphere. The mines were launched into the ocean complete with a heavy bottom anchor, to which the mine was fixed by a sturdy mine anchor wire. After the mine had sunk to the sea-bed, the mine anchor wire was mechanically released and the mine being buoyant, then floated towards the surface until the operating depth, governed by the length of the anchor wire, was reached. Once the operating depth was taken up and the wire taught, the mine armed itself after a short delay by the opening of a safety switch, thus completing the mine electrical firing circuit.
For operational effectiveness and economy the mines were laid to a specific pattern, depth and distance depending on the Mark of mine. The mines were laid in rows at varying depths relating to whether the intended target was to be surface or submerged. The effective range of the mines could be increased by fitting an antenna wire, either floating on the surface or suspended below the mine, on contact with the antenna by a vessel a small electric current was generated by galvanic action which closed a sensitive relay in circuit with the firing battery and thus detonating the mine charge.
Once armed, mine functioning was either by direct contact, magnetic or acoustic influence or a combination of these methods. All British mines were fired by battery; a low value electrical current generated by the appropriate influence through a sensitive relay switch enabling a firing current to be passed to an electric detonator. In some cases the life of the mine was governed by an electric “sterilisation” clock, which after a pre-determined period of time caused an electric current to be passed to a small explosive charge. On detonation of the charge a hole was punched in the mine casing to allow the ingress of water and the eventual sinking of the mine. If the mine broke its anchor prematurely i.e. before the sterilisation clock had run down, the safety switch would close at the loss of tension and so disable the firing circuit, thus reducing the risk to friendly vessels from drifting mines.
This system however, was not infallible, and some vessels were sunk by floating mines, other mines drifted to land, where although safe became “live” as the trailing anchor wire became snagged on rocks and obstacles in the shallows, thus re-opening the safety switch and re-activating the mine firing circuit. During Operation “SN” the mines used were constantly being modified and improved to suit the operational conditions and environment, and by the end of WW II technical developments both in Britain and the United States lead to substantial advances in mine reliability and design. By the end of Operation “SN” the majority of mines laid out were of magnetic influence type.
The explosive charge in a WW II mine is usually large, the destructive effect underwater being from the blast effects of the chemical reaction known as detonation. In British mines two sizes of charge were used, 227 kg and 137 kg, the larger charge being preferred. The Explosives were loaded into the mine by pouring the molten explosives into the charge barrel, a process in which it is critical for maximum efficiency of the detonation reaction, to ensure that all air is expelled and imperfections not allowed to form within the explosives mass. Once set the explosives barrel was sealed, but for safety reasons the booster charge and detonator assembly were not fitted at the manufacturing stage. TNT was the most common explosive used, but other explosive options were tried such as Amatol, which is a mixture of TNT and the cheaper and easier to obtain Ammonium Nitrate. To increase the blast effect underwater Minol was also used, which is TNT with Aluminium added in a powder form.
The Mine Threat Today
When considering the vast numbers of mines laid during operation “SN” it is not surprising that they can still make an appearance today. It is estimated that at most, 5000 or so mines have been destroyed from the NW and SE Iceland mine barrages during and since WW II by the Coast Guard, British Military and others. The remainder remain lying on the sea-bed, buried on beaches or in some cases high up on land where they have been moved, left and eventually forgotten. But what exactly is the threat, and do we still need to worry about them?
In the first place let us not forget what a Sea Mine is designed to achieve i.e. the destruction of surface and submerged marine vessels by detonation of a large quantity of powerful explosives in their close proximity, causing massive if not fatal damage to the vessel and loss of life to its crew and passengers. Mines as with all military explosive devices must always be treated with the greatest respect, no matter what their age or in what condition they are found.
ICG EOD Pic 2. Booster Tube and Explosives from UK Mine.
Although the mine mechanical and electrical mechanisms may be rotted through the effects of time and exposure to the sea and elements, the explosives will normally remain intact and unaffected, and could in some circumstances become more sensitive through chemical change and reaction to the materials surrounding them.
Today it is indeed unlikely to recover a whole mine, although not unknown as can be seen by the picture below of the Mark XVII and M Mark I mines recently found on the Langanes peninsular. If the mine has been buried in the sand, the low oxygen content of the compacted sand around the Mine can cause the mine to be preserved in an incredibly good condition.
ICG EOD Pic 3. M Mk 1 Mine
ICG EDO Pic 4. Mk XVII Mine
In contrast , mines recovered by our fishing fleet are usually in very poor condition and in the majority of cases it is the charge barrel which finds its way on-board, which being filled with a dense explosive material is far more resistant to the effect of the environment than the outer case of the Mine.
Explosives such as TNT are relatively insensitive, they are normally not hydroscopic, and usually maintain their ability to detonate with the same power as when first loaded into the charge barrel. The more sensitive booster and detonator compositions however, being more liable to change with time to become even more sensitive, do present a very real danger and when all three explosive components are present, the mine is considered to be in an extremely dangerous condition!
Today we must be aware that although the mine may not be able to function as originally designed, it is still a very hazardous and potentially life threatening device. The damage radius from a detonating mine on land can extend to 1500 m for fragmentation effects and depending on the terrain and weather and many kilometres for the blast effects, which acting like sound-waves, can reflect off of local geological features and the lower cloud layers if of sufficient density. The effects of a mine detonating on a trawler need no clarification!
British Control and Observation Mine Fields.
In addition to the mines laid during Operation “SN”, mines were also laid by the Royal Navy in Iceland as a protective measure for shipping finding shelter in Fjords such as Hvalfjord, Seyðisfjord and Eyjafjord. These mines were also of the Buoyant, Anchored variety, but contained no influence firing mechanism and held only the explosive charges as they were controlled from a land based observation and mine firing post. The mines could be electrically fired either individually, in groups or en-masse depending on the operational circumstances and were disabled for the passing of friendly shipping.
Small numbers of German mines were laid by U-Boats off the East and West Coasts of Iceland during WW II. These mines were of the Buoyant, Anchored type, fired by magnetic influence.
Unlike British mines the mine casing was of Aluminium and could contain “Prevention of Stripping Equipment”, which if the mine was recovered and then tampered with, would detonate an explosive charge sufficient to destroy the mine mechanism. The sterilisation clock was set for 80 days for this mine and the explosive charge was 300 kg of Hexanite, an extremely powerful high explosive compound. The German mining effort could not however be sustained and was therefore not successful in affecting allied shipping operations from Iceland.
Mines and Public Safety
Our Seamen are well aware of the dangers a mine onboard a ship presents to both the crew and vessel and the necessary procedures to follow if a mine is trawled. If however, a member of the public finds what is thought to be a mine, then under no circumstances should the mine be approached or touched, the Coast Guard or Police must be contacted immediately, giving name, telephone number and position of the mine.
Today it is common for GPS equipment to be carried, but if this is not available any landmarks or permanent features in the immediate location should be noted, as if the mine has been exposed by tidal activity it may soon disappear! The Coast Guard takes all reports of Sea Mines and all other Military Explosive Devices very seriously and on most occasions personnel from the Coast Guard EOD Unit will be dispatched to the scene immediately, in order to positively identify the item and carry out the necessary render safe procedures.
ICG EOD Pic 5. Mine part buried on a beach in NW Iceland.
The TNT Main Charge can be clearly seen.
The legacies of WW II and Operation “SN” and the subsequent hazard from WW II Sea Mines and other military devices will be with us for some considerable time to come, the rusting object found on the beach or unwelcome addition to the trawl should never be treated lightly, always follow the safety rules and report it, if not for yourself then for the next person, who’s encounter with the item may be less fortuitous!
LHG Sprengjudeild April 2005