When is a mine not a mine?

While diving around Falmouth Bay recently, looking for the lost HM Trawler St Ives, I came across what I thought was a possible bomb. I had seen a similar one before, which I had reported to the Explosive Ordnance Disposal Unit (EODU), who then came to detonate the device. On surfacing, we stored the co-ordinates, there was no way of acquiring an exact position without attaching something to the device, with a straight line to the surface. I returned with some volunteer divers, to help re-locate the suspected bomb. We would also film, photograph and measure it. Then the images could be shown to the EODU, in the hope they could identify it.

We waited until some favourable weather came along. Conditions were not ideal for a while. Eventually there was a hole in the weather just for a day, a small group of us went out on my boat. We dropped into the choppy sea and descended, to look for the object. The device took a while to relocate, due to the in water visibility from the recent weather and the very rough original co-ordinates. Once relocated, the remaining dive time had been considerably shortened, the visibility wasn't great and the surface conditions were worsening. The dive was called off, we would have to return.

A few days later, the weather forecast was much improved, so we planned our returned. On arrival, the surface conditions were greatly improved compared to our last visit. I jumped in with my buddy for the day, Sue Barnes, then descended to the sea bed. Within five minutes we were on the device, we photographed and filmed the object before I marked the site with a buoy. After the dive, the second buddy pair of David Gibbins and Katrina Mace, went down, to take even more photographs. After the dives, we discussed what we had seen. We all believed it was highly probable that it was a parachute mine, possibly a type GC with it's end cap still in place. We arrived back on shore late that evening, so waited until the following morning to contact the authorities.

Early Wednesday morning, I called the MCA, they requested some photographs or which we had many. The MCA then passed them onto the EODU. On seeing the images, the EODU rang me and stated that it needed looking at, to see if it was indeed a potentially dangerous device. They were loading up and would be down within two hours.

The EODU arrived at Maenporth Beach, the closest place to the device to launch their boat. After some starting issues, they made their way out. One of their divers went in. We all waited to find out what the device was. Time passed slowly on that cold afternoon. Eventually the EODU diver came up, the boat returned. The C.O. stated that it was in fact a parachute mine, type GC. There was not enough daylight to continue with a disposal, they would have to return the following morning.

On Thursday morning, the EODU left Falmouth on their boat, followed by the RNLI, the harbour master and the harbour pilot. The EODU sent a diver down, while the other boats kept all other vessels at bay. On the shore at Maenporth, several dozen people waited patiently for the detonation. The EODU's boat moved away. A small column of water shot up, followed a few seconds later by a short bang. Everyone looked at each other, “was that it?” was heard echoed amongst the onlookers. Surely not? Compared to the last detonation five years ago, this was a bit of a damp squib. Everyone kept watching and recording. The EODU returned to the location, a diver descended. Fifteen minutes later, all the boats were off, that was it. The MCA told us, that the EODU had declared that it was now safe.

Bemused about the events, we discussed what had happened. We can only assume that the mine came down so fast, without the parachute deploying, that it damaged the internal working and cracked the watertight casing. Seventy five years of salt water ingress, may have caused the explosives to be harmless.

I was asked for a quote by the media, I said “I suppose I should now go and look for the other two I have previously seen now”.

From the first time I spotted the device, I wasn't 100% sure what it was. I had seen a parachute Mine type GC before and this looked very similar but I couldn't work out what the difference was. I assumed it was because it was deeper, and the covered of weed was more dense. When I found the last mine, I pulled some sea weed off to try and look for any markings. When I met the EODU, they told me that the mine would still be live. When it was blown up, it certainly looked more 'live' than not. With this device, I didn't want to pull any sea weed off, just in case. Something in my head said “it wasn't right”. The following day, I dragged a few of my divers back out. My shot-line had gone, either blown up or removed. Luckily I had accurately saved the co-ordinates when I put the shot line in. I dropped my shot and went back down the line with David. What I saw was confusing. What I saw was made of concrete. The nose area was full of iron and steel pieces. There was a bar through the centre, with circular plates along it's length. Had it all been for a lump of concrete? We came up after a short dive and told the others on the boat, we then headed off to a different dive site for a dive.

Finding out it was concrete was disappointing. The following morning I received a message from David, with a link. The link was to a section of a book, with an apocryphal story from WWII. It stated that during WWII, the RAF was running out of mines. The lack of explosives to make more mines was causing a major shortage. Then someone came up with an idea. The magnetic parachute mines rarely actually sank anything. What they did do, is restrict shipping until the mined channels were cleared. While the shipping was backing up outside the port, they would be easy targets for RAF bombers. According to the story, the Germans strapped the fakes bombs to the bottom of their planes, then dropped the fake bombs into the Thames. The mine clearance team working in the Thames were rather confused, pulling up concrete bombs, written on them 'with love from the RAF'. There are other references of fake mines being dropped by both sides. So, was this a fake German mine? We needed to go back.

A few days later, we returned once again. David descended first, to get some photos for a 3D photogrammetry trial. I followed after a short while with Jan, we collected some of the iron and steel pieces we found around the nose. We also managed to recover the reinforcing bar, as well as a piece of steel I had seen wrapped partially around the object. We sifted trough the pieces. There were some interesting objects including springs, U bolts, nuts & bolts, a chain, a cylinder valve and even a glass candlestick holder. Some of the items dated back as far as 1910, what you would expect from a scrap metal pile in 1940. The reinforcing bar had no visible markings on it, the circular discs were very well cut. I measured the steel bar and discs, the bar was 25mm and the discs were 13mm thick. The U.K. was still imperial then, as was the U.S., whereas the rest of Europe including Germany would have been metric. The steel band had steel plating attached to it, it appears to be part of the mine casing. The real type GC mines were aluminium and well made, the piece of steel was roughly cut, not made to the same standard as the real GC. The piece of steel also had some black paint left on it, trying to make it look like a real type GC mine. The scrap metal in the nose would have made it fall nose first, unlike a plain lump of concrete. Another effort to make it look and appear, real. It fooled the British back then, it continued to fool us until this day.

The fake mine was the first one we know of that has been found and identified, around the Falmouth area. During WWII Falmouth was extensively mined, so much so, that in 1940 the port was closed several times due to the amount of shipping loses. Most of the mines and fake mines would have been cleared during mine clearing operations, this particular fake mine was out of the normal shipping channels. It was probably missed, like the real one I found in the mouth of the Helford five years ago.

This type of parachute mine was intended to look like a Luftmine B (LMB), called a Type C by the British Admiralty. The Luftwaffe started dropping these mines around the UK some time in November 1939 were being, from Heinkel He115s and He111s.

Physical description

A German Parachute Mine is a thin wall cylinder 25in in diameter, 86in long, with a hemispherical nose. Fully filled, it would have weighed about 2176lb, of which 1536lb was explosive. The mines were cylindrical in shape with a hemispherical nose, and deployed under a 27ft diameter green artificial silk parachute, falling at about 40mph. They were fitted with magnetic firing and later with acoustic or magnetic/acoustic firing. When the mine hit the water and sank to more that 8ft, hydrostatic pressure and the dissolution of a soluble plug actuated the magnetic device and the mine became operational against shipping. The mine was also armed with a clockwork bomb fuze which caused the bomb to explode when used against land targets, and this was started by the impact of hitting the ground. The mine was timed to detonate 25 seconds after the fuze had started. When deployed at sea, the time fuze did not operate as a diaphragm stopped the clockwork when under the pressure of 7 feet of water or more. The first intentional use of magnetic mines against land targets was on the night of 16 September 1940, when the mines with their charge/weight ratio of 60 - 70 % explosive caused considerable blast damage in built up areas. Inevitably, they became known to the British populace as 'Land Mines'.

Historic notes

Information from old IWM caption: 'The mine could also be fitted magnetic, acoustic or magnetic-acoustic units, and also be used a time mine or a depth charge. It could be armed by means of a hydrostatic clock which operated when immersed in over eight feet of water and could be set to render the unit active from 15 minutes to six days after the mine was laid, or could be used to detonate the mine after a set period by a hydrostatic switch which completed a circuit and detonated the mine when it was immersed in 40 to 50 feet of water.'

The Second World War period German land and sea mines. There were two types of magnetic sea mines used by the the Germans, who termed them the Luftmine A (LMA ) of 500kg, and the Luftmine B (LMB) of 1000kg. They were known by the British Admiralty as the Admiralty Type D and Admiralty Type C respectively. This is an example of the larger mine. The Luftwaffe began dropping magnetic mines into the waters around Britain during November 1939, first from He115 and He111 aircraft. The mines were cylindrical in shape with a hemispherical nose, and deployed under a 27ft diameter green artificial silk parachute, falling at about 40mph. They were fitted with magnetic firing and later with acoustic or magnetic/acoustic firing. When the mine hit the water and sank to more that 8ft, hydrostatic pressure and the dissolution of a soluble plug actuated the magnetic device and the mine became operational against shipping. The mine was also armed with a clockwork bomb fuze which caused the bomb to explode when used against land targets, and this was started by the impact of hitting the ground. The mine was timed to detonate 25 seconds after the fuze had started. When deployed at sea, the time fuze did not operate as a diaphragm stopped the clockwork when under the pressure of 7 feet of water or more. The first intentional use of magnetic mines against land targets was on the night of 16 September 1940, when the mines with their charge/weight ratio of 60 - 70 % explosive caused considerable blast damage in built up areas. Inevitably, they became known to the British populace as 'Land Mines'.