The British mine offensive opened in 1939 when Royal Navy surface ships and submarines laid the devices in the North Sea, the German Bight, the Skagerrak, the Kattegat, off Norway, and later in the English Channel. The Royal Air Force Bomber Command began minelaying from the air in April 1940, but a lack of long- range aircraft limited mining to areas near British bases. In 1942, however, Air Chief Marshal Arthur Harris, the new Commander-in-Chief of Bomber Command, made more long-range bombers available, extending the campaign from the Biscay and Channel ports to the North Sea and the western Baltic. With the advent of the Lancaster in 1943, the whole German Baltic coast up to the Gulf of Danzig was in danger of being mined.
The first such devices had magnetic detonators designed to explode and break a ship’s keel when its magnetic field passed overhead. The British deployed a mine with an acoustic exploder in August 1942. Both types together served to confuse German countermeasures. Against these mines the Germans employed a towed Kabel-Fern-Raum-Gerat (KFRG) fed by a diesel generator. It produced a magnetic field that exploded the mine after the degaussed minesweeper had passed unharmed. The Germans used Gerauschboje Toni (GBT), or rattler box, as a noisemaker to counter acoustic mines. Sperrbrechers were equipped with a Voraus Eigen Schutz (VES) device, which was a long cable slung around the fore part of the ship and fed by current from a generator to produce a magnetic field some distance ahead of the Sperrbrecher, exploding the mine before the degaussed ship reached it.
In late 1942 the British began to develop special types of mines with circuits that could detect the difference between the magnetic signature of a minesweeper and a normal ship. The mine had a sensitive magnetic unit activated by a strong magnetic field. But it did not detonate until the unit recognized a normal field. Another type, intended to combat Sperrbrechers, featured a clock that started when a magnetic field activated it but delayed the detonation from 6 to 16 seconds, when the ship was passing overhead. One especially complex development was a magnetic mine with a clicker circuit where no detonation would take place until the preset number of activations had occurred. These could range from 5 or 10 up to 64.
A new problem arose when Bomber Command began dropping mines not only in shipping lanes along the coasts, but also in river estuaries and harbor mouths. We needed smaller Sperrbrechers with good maneuverability, but it was difficult to load all the necessary equipment into a small coaster. German Navy officials undertook investigations to find a workable solution.
By chance, experts in Germany heard about an experiment by the Italian Professor Dr. G. M. Pestarine, in which he had put iron cores with a cable coil winding across each other on the fore part of a wooden vessel and had achieved good results with this Canona Anti Magnetica (CAM). In 1943 the Kriegsmarine purchased two such devices and sent them to the Mine Test Command for evaluation. It seemed possible that a CAM could be installed in a moderate- size vessel with an iron hull.
The Netlayer Test Command had just such a vessel, the Martha. Launched in 1900 as a seagoing barge, in 1920 the ship was rebuilt as a coastal freighter of 546 gross tons. At this time she received two triple-expansion 600-horsepower engines, able to achieve up to 9.5 knots on paper but only 8 knots in water. On 4 April 1942 the German Navy commissioned the Martha a test vessel and subsequently assigned her to the Netlaying Force Kiel.
The Martha was rebuilt at Aarhaus, Denmark, as a test Sperrbrecher for the CAM equipment. She had a length of almost 60 meters, a beam of a bit more than 8 meters, and a draught of 2.5 meters. Forward was a big cargo hold, used to house the diesel generator on a shock-proof foundation. On the deck above the hold, the lamellar iron antimagnetic CAM cross with its cable coiling stood on a wooden base. Because its beam was broader than the ship’s, four outriggers had to be fitted for the ends of the crosses. On top of the cross stood a Flak-stand mounting a 37- mm antiaircraft gun. The old crew quarters were between the diesel room and the engine spaces aft. As the crew consisted of more than 60 men—rather than the freighter’s 12—the quarters were much too small. Thus, shipbuilders erected a two-story superstructure on the after half of the ship. The lower deck housed the chief petty officers, the coxswain, and the engineers, along with the administrative compartment. On the upper level were the navigation bridge—which resembled a destroyer bridge with armored shutters for the windows—the charthouse, the wireless room, and quarters for the captain and some other officers and midshipmen. A spacious signal deck, used mostly as a sun deck and crowned by a light tripod mast topped off the upper level. On the sun deck were two stands for one 20-mm antiaircraft gun each; at the after end was a third such stand, equipped later with a 20-mm quadruple gun. All this additional equipment led the ship’s freeboard to drop from about 3.3 meters to about 1 meter. The additional draught reduced top speed to about 6 knots.
On 14 August 1943 the Martha was commissioned as Sperrbrecher 104 by her commanding officer, Kapitänleutnant der Reserve Rudolf Baffy, a veteran of World War I. After her initial trials the vessel was allocated on 1 September 1943 to the 2. Sicherungsflottille—2nd Security Flotilla—at Swinemünde. The voyage there provided an opportunity to test her seaworthiness; the crew learned quickly that she was difficult to handle in wind and seas above Beaufort 4-5, because she shipped a great deal of water from the low-lying outriggers and gave way when a strong wind came from the side. The Sperrbrecher then “sailed,” and the skipper or watch officer, as well as the helmsman, needed a great deal of experience to hold her on course.
During this period, I was a midshipman training as a submarine watch officer. In March 1944 my class took a course at the antiaircraft school at Swinemünde. We received hands-on instruction on board a tank landing craft that had been equipped as an antiaircraft-training vessel. One sunny day on the way to practice firing at targets towed by an old Junkers W-34, we noticed a curious vessel going back and forth along the buoy lines at the anchorage. Suddenly a big explosion erupted between us and this ship, which we were told was Sperrbrecher 104. We thought she might sink, but instead she steamed on as if nothing had happened, blinking to the signal station at Swinemünde to report her first sweeping success.
I could not imagine that only four weeks later, after finishing the submarine course, I would be ordered to the ship we had made so many jokes about because of her strange appearance. On the morning of 19 April another midshipman, J. von Rodbertus, and myself had just reported on board when the captain of Sperrbrecher 104 gave the order to leave harbor.
The night before, Bomber Command had flown a big raid, dropping more than 600 mines, many of them in the Pomeranian Bay north of Swinemünde. The anchorage, Lane 51 from Swinemünde to Sassnitz, and Lane 53 to Kolberg were closed, and all vessels of the 2. Sicherungsflottille set out to sweep the lanes so traffic could resume. Of the ten mines exploded that day, Sperrbrecher 104 detonated five.
After rounding the mole head covering the exit from the Swine River, we made one run along Lane 51 to support the trawlers Vs 205 and Vs 201 running ahead with their towed magnetic-field sweeps. At 0538 we heard in the distance the first mine being blown up by Vs 205. At 0601 it was our turn. At 650 meters ahead, a big column of water erupted to starboard, and a heavy bang resounded against our ship. Shortly after our report, we were recalled to sweep the anchorage outside Swinemünde. There we went back and forth laying a line of buoys until we had accomplished the necessary number of runs to have the exact distance for the next line of runs. In six hours we swept four more mines, the first at only 50 meters, the next two more distant. Then a mine exploded only 30 meters from our starboard bow, giving the ship a shock. Although the blow did not damage the strongly built hull or the engine, it caused some breaks in the insulation of the cables in the VES equipment, so we had to go for the Oderwerke at Stettin for repairs.
On 26 April we returned to Swinemünde in time to give the numerous merchant ships blocked at the anchorage minesweeping escort to enter the harbor and then to make a final check on Lane 51 before allowing it to reopen. But the clicker devices of the mines were still switched off during our efforts, and on 27 April the U-803, heading for Swinemünde along the western border of the anchorage, hit a mine and sank, taking nine men down with her. So during the next two days we had to run our lines across the anchorage again, sweeping one mine a day.
Early in May heavy seas swamping our outriggers damaged the insulation of our VES magnetic cable equipment. We had to spend four days in the Oderwerke. When we got back on 16 May we immediately received orders to check the area where the target ship Hessen was cruising under remote control during gunnery training for cruisers and destroyers. Again, two mines detonated very close by, the first at 25 meters, the second only 12 meters off our port quarter, causing a rupture of the engine’s steam-off ducts, which were repaired at the Marine Ausrüstungs Betrieb at Swinemünde. On 20 May we returned to continue patrolling the Schiessgebiet Hessen—Firing Range Hessen—exploding nine mines between 22 and 29 May.
While we were running along our lines, flying signals to show our right of way, a U-boat tried to cross ahead of our curious-looking ship in disregard of the signals. Suddenly, a mine exploded between us, which was already a routine event to us. We made a blinker signal to the station ashore, giving the position of the sweeping success, and then all of us on the bridge waited for our coxswain to come up to present the list of all the “broken” bottles of wine and brandy. Of course, after suffering “heavy losses” during the explosions of our first mines, he had constructed a shockproof store for this very important stuff. But because we were a happy ship and liked very much to relax with a few bottles after coming into port, we needed a greater supply than we normally got. So any mine detonation led to “broken bottles” that we could replace from the supply depot. As we were studying the list, our signalman read out a blinker signal from the U-boat: “Captain to Captain, may I go ahead again?” A roar of laughter exploded on the bridge. We all felt a little proud.
After a week in the Oderwerke to repair some defects in the old engine, on 7 June we set out to check the lane from Swinemünde to Sassnitz, where some delayed-timer mines were still becoming active. We exploded one the next day. On 12 June we were returning to Swinemünde, when a short distance ahead a black spout of water and white steam blew off around the trawler Vs 201, which started immediately to capsize. We anchored and lowered our motor- boat to rescue the survivors. Two days later we were again at sea to clear the channel between Lanes 51 and 53 and blew up one mine each on 14 and 15 June. The last, at only ten meters, caused sufficient damage to send us back to the Oderwerke for repairs.
On 22 June we resumed our task and on the next day blew up our 23rd mine. Upon our return to Swinemünde the Befehlshaber der Sicherung der Ostsee (BSO)—Commander of Security Forces, Baltic, Vice Admiral Hans Stohwasser, came to inspect our ship and decorate crew members who had achieved the necessary 100 points with the Minesweeping Badge. The interlude was a brief one, and from 28 to 30 June we were back searching for mines.
In July we served as a mine escort in connection with salvage operations for ships sunk by mines. We escorted a diving barge on 3 and 4 July to the place where the lugger Vs 217 sank. We then escorted the tow of the wreck of Vs 201 to Swinemünde. After a check of the Schiessgebiet Hessen on 7 July, we made a trip to Sassnitz to give a tow with an aircraft dock mine escort. Next, we had to sweep an area east of Rügen in preparation for the salvage of the U-1013, which had sunk after colliding with the U-286. From 13 to 16 July, we escorted a tow with two salvage barges to a wreck off Palmerort. For the first time, we had to enter the complicated narrows of Greifswalder Oie, the Ruden, and through the Greifswalder Bodden to Stralsund. On our way we saw a V-l missile launched from Peenemünde suddenly start to go wild and come down not too far from our ship. Another missile flew accurately.
From 19 to 29 July, Sperrbrecher 104 had to check the Schiessgebiet Hessen and then to clear the entrance from south of Greifswalder Oie into the Bod- den, sweeping one mine on 28 July. In the evening we always anchored to the south. One night for the first time we heard a thunderous roar and saw a burst of flame when a V-2 rocket launched nearby. We had often observed the exhaust trail of these rockets during test firings. Our clearance of the area allowed the antiaircraft ship Undine—the former Dutch coast defense battleship Jacob van Heemskerck—to be anchored there again to defend Peenemünde. In one incident, this ship engaged a formation of U.S. B-17 bombers with her radar-controlled 105-mm guns, and we could see the puffs of shells exploding in the midst of the formation, while several bombers came down in flames. We rescued some survivors who bailed out and fished up a number of their fine silk parachutes.
From 7 to 11 August, we had to check and sweep Lane 51 from Swinemünde to Sassnitz, exploding one mine on 9 August. From the 13th to the 16th we searched for the wrecks of two small vessels, the Orkan and the Obra, sunk by mines not far from Greifswalder Oie, and then returned to Swinemünde.
In June and July the RAF had directed its mine offensive against the French and Belgian coasts in support of the invasion of Normandy. In August the campaign was stepped up and directed mainly against the Baltic. The first big operation occurred on the night of 16-17 August, when 49 Lancasters dropped 172 mines north of Swinemünde and into the “Kaiserfahrt” and the Stettiner Haff.
Again all the shipping lanes around Swinemünde had to be closed and an all-out minesweeping effort begun. Sperrbrecher 104 departed immediately after the “all clear” to check the harbor and then to proceed into the Kaiserfahrt where a mine had already sunk the Kriegsfischkutter 510. From 0809 to 1808 we raced back and forth in the Kaiserfahrt and the Stettiner Haff and blew up no fewer than nine mines. The last one exploded in shallow water only five meters ahead of our bow, splashing a big column of black mud and water down on us. Some leaks developed in the forepart of the vessel down in the anchor locker below the paint locker. Paint buckets were rolling around in the locker and leaking, covering the rising water with rainbow colors and emitting a strong smell and poisonous gasses. Another crew member and myself had to dive into the anchor locker to try closing the leaks, which were mostly dents in the plating and sprung bolts. Meanwhile, on deck pumps began doing their work, and we could come up after partly completing our task, covered with paint and somewhat tipsy from the smell. We washed each other with petrol while our ship returned to Swinemünde, where we hoped to go ashore as quickly as possible to escape the odor of paints, petrol, and oil. But when our ship was secured and we were ready to leave, a message arrived stating that the BSO, now Rear Admiral Hans Bütow, was coming to thank the crew for the day’s achievements and decorate some of its members. So we had to stay.
Two days later our ship was sent back into the Haff. We blew up three more mines before being ordered to the Stettiner Oderwerke, where we entered the floating dock to plug the leaks in the forepart of the ship and repair some shock-damage to the VES equipment.
On the night of 29-30 August, Stettin became the target of RAF Bomber Command. A total of 383 Lancasters dropped 610 tons of high explosives and 731 tons of incendiaries. Watching from the bridge of our ship in the floating dock we could see the Christmas-Tree markers drifting to earth west of the city. Then the bombs screamed down, and the explosions came nearer and nearer. One bomb exploded on the slipway on one side of our dock, the next in the water on the other side. Like blowing a whistle, air escaped from leaks in the fore part of the dock, where a big ocean-tug was lying. We ran down to cut the hawsers that secured both dock parts and happily observed that, while the fore part began to sink, our part remained afloat. When the screams and explosions of the bombs died down, fires sprang up everywhere. After the all-clear signal we formed fire-fighting parties to assist the yard fire- brigade in trying to extinguish the fires raging in the workshops and buildings of the yard area. The next morning it was a terrible sight to walk through the streets with the walls of the burned houses and all the debris and damaged belongings of the ausgebombt—“out bombed”—inhabitants lying around.
That same night the RAF dropped mines in the Baltic. The dock-workers, aided by our crew, had to work hard to bring our ship into operational status, but on 2 September we left the still smoking harbor of Stettin for Swinemünde. After taking on supplies, we started to clear Lane 51 from Swinemünde to Sassnitz and the Schiessgebiet Hessen. It took five days of steaming back and forth before the first two mines blew up on 10 September, followed by one more on the 11th and two on 13 September. Two of these mines were very close, one only five meters and one ten meters ahead, causing small leaks forward and sending us back to the Oderwerke for repairs.
During September the RAF continued its mine offensive in the Baltic, dropping 415 mines in the shipping lanes from Kiel to Cape Arkona, off Swinemünde, and into the Gulf of Danzig. The drops were accurate, because the Lancasters used radar to locate the buoys, which were easy to detect in normal circumstances. On the other hand, German radar stations ashore could follow the planes and often locate the drops fairly accurately. Thus, in many cases we knew where to search for the mines, but it took many runs before we could finally activate their detonators by recording the preset number of magnetic fields. To sweep the acoustic mines, we used not only the Gerauschboje Toni but also the Knallkorpergerat, a tube going down into the water into which a crew member fed small explosive charges, making a noise we hoped would activate the detonators of the acoustic mines.
On 24 and 25 September we had to check the lanes into the Stettiner Haff and on the 26th we started to patrol from the War Location Beacon off the Swinemünde anchorage along Lane 51. On 29 September we had another success and after a short spell in Swinemünde blew up our 45th mine on 3 October. Three days later we were just east of Peenemünde when a squadron of U.S. bombers flew over us on the way to this important target. We opened fire with our 37-mm gun, but we could not reach the planes.
After the Soviet-Finnish truce in September the Finns had to escort Soviet submarines through the mine-and net- barrages in the Gulf of Finland. We realized this when we read “Enigma”-enciphered messages about submarine attacks on ships supplying the Courland army, which had been encircled by the Soviet breakthrough to the Baltic coast early in October. The following month several ships were sunk or damaged by Soviet mines laid by submarines off Cape Arkona and Stolpmünde.
As these losses occurred outside the area of operations of Sperrbrecher 104, we were not overly concerned. So we continued our patrol along the usual shipping lanes.
In December, I was promoted to ensign and had to transfer as executive officer to the M 502, one of the old black minesweepers from World War I assigned with her sister ship, M 545, to our flotilla. We became busy in late December 1944 and January 1945 after new British mine drops. Our sweeping efforts with our towed KFRG, two towed GBT and one GBT fixed on a dip-spar at the bow were hampered by severe winter weather with snow storms and ice. Losses and damage to our ships increased, and the closing of the swept lanes caused heavy congestion in harbors and anchorages. Sometimes dozens of ships waited in the anchorage off Swinemünde for the “all clear.” While British air-laid mines caused trouble for German minesweeping forces and shipping and seriously delayed the training program for the new U-boat Types XXI and XXIII, there was also a positive result: Soviet submarines avoided the central Baltic and the shallow waters off the Pommeranian coast, which were heavily mined. Thus, the British minefields provided antisubmarine protection for the anchorages where submarines could have sunk a huge amount of tonnage without much risk.
On the dark night of 26 December we were escorting a group of ten U-boats through a snow storm to Swinemünde when a Type XXIII boat, U-2342, struck a mine and sank immediately. Once we realized what had happened we secured our sweeping gear, with buoys so we could pick it up later, and launched our cutter to try to rescue the men who had been able to escape the sinking U-boat. This had to be done quickly, because no one could hold out for more than ten minutes in the icy water. The other U-boats could do nothing; their rounded hulls were covered with ice and nobody could move on their decks. Our cutter was able to pick up seven almost frozen survivors; superhuman efforts revived five, but two were beyond help. Five others had gone down with their boat.
In January 1945 the great Soviet winter offensive led to the biggest waterborne evacuation in history. From Prussian ports all available ships—heavily overloaded with civilians, wounded soldiers, and nonessential military personnel—tried to reach ports in the western Baltic and return east to take on new refugees. Several times we had to escort up to four or five big liners and freighters, crowded to the last space with people going west or returning empty to the east. We escorted the hospital ship Berlin, which, after emptying her human freight into hospital trains at Swinemünde, was to steam east to Kolberg. Just as we passed the War Location Beacon, we heard a hollow detonation and a column of water shooting up the side of the Berlin indicated a mine detonation. The captain tried to take her out of the swept channel to keep from blocking it for other vessels. But two more mines exploded, causing the ship to settle to the bottom, leaving the decks and the superstructure above water. It was great luck that she was empty. The night before, as we learned from radio signals, a Soviet submarine had sunk the liner Wilhelm Gustloff-, between 5,200 and 5,400 people perished in the greatest maritime catastrophe of all time.
Continuous operations had caused many defects in the old M 502 and it became necessary to send her into the Danish yard at Frederikshavn for repairs. There I received new orders as a company officer in the 2. Marine Grenadier Division then being organized in southern Schleswig- Holstein. After it took form, I was sent to a Battalion Leadership Course, where experienced army officers trained us in land warfare, especially the use of modern weapons such as the shoulder-fired Panzerfaust antitank rocket. On 14 April, during our defense of the village of Hohenaverbergen, I had to use the Panzerfaust against flame-throwing crocodile tanks of the British 7th Armoured Division. The war was then in its last gasp and our unit was included in the capitulation of northern Germany on 4-5 May.
