The Luftwaffe's Minensuchgruppe 1 (MSGr 1)—widely known as Sonderkommando "Mausi"—was a specialized airborne mine-sweeping unit formed in late 1940 to trigger and detonate British magnetic sea mines using modified Junkers Ju 52/3m aircraft fitted with massive electrical energizing rings. "Mausi" was short for Magnetspule or magnetic coil. Peter Kassak provides some details of mine-clearing operations flown by the Luftwaffe's specialist Ju 52 mine-sweepers along the Danube as the Allies sought to interdict German oil supplies ..
The recent hot weather throughout Europe (summer 2026) has caused a significant drop in river water levels - even in one of the largest rivers in Europe, the Danube. And the low water levels have exposed some long-hidden WW II relics. Aside from the wrecks of ships in Serbia, or Hungary, there was also ammunition of various types located on the banks of the river. In the southern Slovakian part of the river (the river is a border between the Slovak republic and Hungary) two RAF mines were located and detonated on 3 August causing the suspension of river traffic on the Danube for several hours. Given the location near the village of Virt, the British sea mines most probably originated from the “gardening” mission flown on 29 May 1944 by the RAF's 205 Group and its 178 Squadron Liberator crews. The Wellington and Liberator crews had to sow their mines (hence the slang term 'gardening') at low level on moonlit nights, running the gauntlet of night fighters, flak and balloon barrages.
Below; British 700 kg anti-shipping mines found in the Slovakian section of the Danube river, August 2026, source: Police of the Slovak republic FB page.
During WWII, the smooth functioning of the Danube river transport system was crucial for Germany, and its disruption was highly desirable. Two main options presented themselves to Allied planners in Italy. One involved the destruction of the oil refineries, port facilities and other infrastructure. The other required the interdiction of Danube river traffic by mining. Both options would be resorted to as the USAAF and RAF sought to cut Germany off from its much-needed Romanian oil.
The first attempt to disrupt Danube shipping was undertaken by the Russians in September 1941, when Soviet commandos penetrated the German lines from Bessarabia and dropped drifting contact mines in the river. These were however ineffective, damaging no ships although several were struck by them. Traffic was halted for 12 hours only. The first attempt by the Western allies to hinder the supply of Romanian oil to Germany was undertaken on 12 June 1942, when B-24 Liberators of the USAAF’s HALPRO detachment attacked the oilfields at Ploesti. However, the main “gardening” campaign was performed by RAF 205 Group between April to October 1944 and had the most impact. It is estimated that between April and October Allied mines caused a reduction of at least 60% in Danube priority traffic, while ordinary commercial traffic suffered still more seriously to the extent of complete interdiction in certain categories.
German counter measures involving the Luftwaffe were essentially two-fold - night-fighters were scrambled almost nightly with some noticeable results during late summer 1944 (also described in the latest book from AWP, "Nachtjagd over the Eastern Front"). The second counter measure involving the Luftwaffe was the deployment of mine-sweeping aircraft. MSGr 1 Ju 52s swept the river about four hours daily, usually in the early morning and again in the evening. These times were chosen because experience had shown that Allied fighter planes were least likely to appear then. It is believed that 165 mines were detonated by the aircraft.
Below; Ju 52 MS version flying over the bridge in Bratislava in summer 1944, source Dusan Bublik
DW 1 (Directional Wireless 1) was the RAF codename for a magnetically energized (degaussing) ring some 50 feet in diameter, fitted to some Mark I Wellington bombers and used to sweep magnetic sea mines by detonation. The aircraft flew low over the sea; the mines were detecting the magnetic field of the DW 1 and exploded accordingly. The crew of the Wellington were successful in destroying a magnetic mine on their very first sortie on the 8 January 1940 (aircraft was P2518 piloted by test pilot ‘Bruin’ Purvis, navigator Lt.Cdr. ‘Ben’ Bolt with Sq/Ldr. John Chaplin operating the gear in the fuselage). The Germans adopted the idea and fitted similar degaussing devices and rings to a number of Ju 52s. The Ju 52/3m g4e MS (Minen Sucher = mine finder) was fitted with a large Dural hoop braced beneath the wing and fuselage. This hoop was energized by an additional motor installed in the fuselage. The magnetic field generated thus triggered magnetically fused mines.
The advantage of the Ju 52/3m for mine-sweeping operations was that it was easy to bring into action at various locations, and over remote areas. It could search for mines that were undetected by conventional water-borne mine sweepers. But there were also disadvantages. The radius of effectiveness of each aircraft was only about 50 metres. Operations could not be undertaken in bad weather and low visibility because the strong magnetic field produced by the mine degaussing equipment caused on-board compasses to malfunction. And the aircraft’s armament was weak, and insufficient to defend the crew if attacked. However, the machine had an endurance of around four hours at an average speed of 180 km/h.
The M-devices featuring the huge MS ring (MS-Magnetspule) mounted under each aircraft were of course used for exploding magnetic mines. Other types of mines were acoustic. For sweeping , the so-called A-device (A for Acoustic) was used. Once installed in the Ju 52/3m, the acoustic device continuously changed channels and radioed various wavelengths, which triggered mines to explode. ELM/A mines were sensitive within 2200- 2600 meters and detonated at 600-800 meters from the source of the signal. ELM/A-St mines were sensitive within 600-800 meters and detonated at 200- 300 meters from the source. The signal wavelength was changed every 30 seconds, and was organized in 10 channels. In some cases, both magnetic and acoustic mines were dropped by RAF crews. Therefore combined formations of Ju-52/3m mine sweepers could be flown - aircraft carrying the M-device flew ahead, one aircraft carrying an A-device following. The distance between the planes varied according to flight speed and height, to prevent damage to following aircraft by the delayed detonation of a mine.
At the beginning of April 1944, the unit had only one aircraft, but received 17 more during the month. In June one aircraft was lost to US fighters. This happened on June 6 north-west of Turnu Severin, Romania, where 1st Lt. James W. Stegman of the 82nd FG/96th FS claimed a Ju 52 with a strange ring device under the fuselage. This correlates with the loss of Ju 52/3m MS W.Nr. 501313 at location 44°46’ N, 21°32’ E. Its crew consisted of pilot Lt. Oskar Fuhrmann, observer Flg. Heinz Rietzsch, Onboard mechanic Ofw. Franz Bußkamp and gunner Fw. Max Muchowski. All four were KIA. 3./MSGr.1 ended the month of June with 24 aircraft. Four more Ju 52s were lost through enemy action in July. Three losses occurred on July 4th, when three pilots, 1st Lt. Walther J. Carroll Jr., Capt. Richard M. Gangel and 1st Lt. Arthur W. Kidder Jr., all of the 96th FS, 82nd FG each claimed a Ju 52 with a ring device shot down north west of Craiova, Romania. The losses were however made up and the strength of the unit remained 24 aircraft. August brought one loss due to enemy fighters, which was replaced. The only recorded loss of this unit for August, however, was due to a mine explosion. It occurred on 4 August and three men on board the aircraft died. On 25 August 3. Staffel of MSGr. 1 moved to Belgrade from Rumania. September 1944 was a disaster for the unit as 10 Ju 52/3ms were lost due to enemy action, with three more in October. The only loss we could identify occurred on 5 October, when a Ju-52/3m MS was lost at Dunaremete at km 1826 at 16:04 hours. Again, the cause was a mine explosion. The four crew were killed (pilot Ofhr. Karl Matula, radio operator Uffz. Willi Hendler, mechanic Fw. Hermann Fritsch and gunner Uffz. Franz Dreßler).
Above; Karl Matula, pilot in a Minensuchverband, killed during a Danube mine-sweeping sortie with his crew at the controls of his Ju 52 on 5 October 1944. Sterbebild, source eBay.com
During WWII, the smooth functioning of the Danube river transport system was crucial for Germany, and its disruption was highly desirable. Two main options presented themselves to Allied planners in Italy. One involved the destruction of the oil refineries, port facilities and other infrastructure. The other required the interdiction of Danube river traffic by mining. Both options would be resorted to as the USAAF and RAF sought to cut Germany off from its much-needed Romanian oil.
The first attempt to disrupt Danube shipping was undertaken by the Russians in September 1941, when Soviet commandos penetrated the German lines from Bessarabia and dropped drifting contact mines in the river. These were however ineffective, damaging no ships although several were struck by them. Traffic was halted for 12 hours only. The first attempt by the Western allies to hinder the supply of Romanian oil to Germany was undertaken on 12 June 1942, when B-24 Liberators of the USAAF’s HALPRO detachment attacked the oilfields at Ploesti. However, the main “gardening” campaign was performed by RAF 205 Group between April to October 1944 and had the most impact. It is estimated that between April and October Allied mines caused a reduction of at least 60% in Danube priority traffic, while ordinary commercial traffic suffered still more seriously to the extent of complete interdiction in certain categories.
German counter measures involving the Luftwaffe were essentially two-fold - night-fighters were scrambled almost nightly with some noticeable results during late summer 1944 (also described in the latest book from AWP, "Nachtjagd over the Eastern Front"). The second counter measure involving the Luftwaffe was the deployment of mine-sweeping aircraft. MSGr 1 Ju 52s swept the river about four hours daily, usually in the early morning and again in the evening. These times were chosen because experience had shown that Allied fighter planes were least likely to appear then. It is believed that 165 mines were detonated by the aircraft.
Below; Ju 52 MS version flying over the bridge in Bratislava in summer 1944, source Dusan Bublik
DW 1 (Directional Wireless 1) was the RAF codename for a magnetically energized (degaussing) ring some 50 feet in diameter, fitted to some Mark I Wellington bombers and used to sweep magnetic sea mines by detonation. The aircraft flew low over the sea; the mines were detecting the magnetic field of the DW 1 and exploded accordingly. The crew of the Wellington were successful in destroying a magnetic mine on their very first sortie on the 8 January 1940 (aircraft was P2518 piloted by test pilot ‘Bruin’ Purvis, navigator Lt.Cdr. ‘Ben’ Bolt with Sq/Ldr. John Chaplin operating the gear in the fuselage). The Germans adopted the idea and fitted similar degaussing devices and rings to a number of Ju 52s. The Ju 52/3m g4e MS (Minen Sucher = mine finder) was fitted with a large Dural hoop braced beneath the wing and fuselage. This hoop was energized by an additional motor installed in the fuselage. The magnetic field generated thus triggered magnetically fused mines.
The advantage of the Ju 52/3m for mine-sweeping operations was that it was easy to bring into action at various locations, and over remote areas. It could search for mines that were undetected by conventional water-borne mine sweepers. But there were also disadvantages. The radius of effectiveness of each aircraft was only about 50 metres. Operations could not be undertaken in bad weather and low visibility because the strong magnetic field produced by the mine degaussing equipment caused on-board compasses to malfunction. And the aircraft’s armament was weak, and insufficient to defend the crew if attacked. However, the machine had an endurance of around four hours at an average speed of 180 km/h.
The M-devices featuring the huge MS ring (MS-Magnetspule) mounted under each aircraft were of course used for exploding magnetic mines. Other types of mines were acoustic. For sweeping , the so-called A-device (A for Acoustic) was used. Once installed in the Ju 52/3m, the acoustic device continuously changed channels and radioed various wavelengths, which triggered mines to explode. ELM/A mines were sensitive within 2200- 2600 meters and detonated at 600-800 meters from the source of the signal. ELM/A-St mines were sensitive within 600-800 meters and detonated at 200- 300 meters from the source. The signal wavelength was changed every 30 seconds, and was organized in 10 channels. In some cases, both magnetic and acoustic mines were dropped by RAF crews. Therefore combined formations of Ju-52/3m mine sweepers could be flown - aircraft carrying the M-device flew ahead, one aircraft carrying an A-device following. The distance between the planes varied according to flight speed and height, to prevent damage to following aircraft by the delayed detonation of a mine.
Below; diagram depicting a mixed formation of M-and A- type mine sweeping Ju 52s
The unit tasked with minesweeping was Minensuchgruppe 1 (MSGr. 1) formed in October 1942. The task of the Minensuchverbände (mine searching units) was to clear sea and river water routes of mines. MSGr.1 comprised six independent Staffeln, which were active in various theatres of operations. To operate over the Black Sea and later the Danube, a 3. Staffel was established in Varna. From February to October 1944 it was registered as an independent 3. Minensuchstaffel, using Junkers Ju-52/3m MS aircraft. For the last two months of its existence, it moved to Neusatz. Each Minensuchstaffel consisted of 18 Ju 52/3m MS aircraft, of which 14 were so-called M-planes and 4 were A-planes. But between June and September 3. Staffel MSGr.1 had 24 aircraft on charge, due to losses and also greater operational demands. At that time, according to some sources, six planes were stationed at Budapest (Budaőrs airport), eleven in Belgrade and seven in Craiova/Walachei. The aircraft carried the code 3K+.
The unit tasked with minesweeping was Minensuchgruppe 1 (MSGr. 1) formed in October 1942. The task of the Minensuchverbände (mine searching units) was to clear sea and river water routes of mines. MSGr.1 comprised six independent Staffeln, which were active in various theatres of operations. To operate over the Black Sea and later the Danube, a 3. Staffel was established in Varna. From February to October 1944 it was registered as an independent 3. Minensuchstaffel, using Junkers Ju-52/3m MS aircraft. For the last two months of its existence, it moved to Neusatz. Each Minensuchstaffel consisted of 18 Ju 52/3m MS aircraft, of which 14 were so-called M-planes and 4 were A-planes. But between June and September 3. Staffel MSGr.1 had 24 aircraft on charge, due to losses and also greater operational demands. At that time, according to some sources, six planes were stationed at Budapest (Budaőrs airport), eleven in Belgrade and seven in Craiova/Walachei. The aircraft carried the code 3K+.
At the beginning of April 1944, the unit had only one aircraft, but received 17 more during the month. In June one aircraft was lost to US fighters. This happened on June 6 north-west of Turnu Severin, Romania, where 1st Lt. James W. Stegman of the 82nd FG/96th FS claimed a Ju 52 with a strange ring device under the fuselage. This correlates with the loss of Ju 52/3m MS W.Nr. 501313 at location 44°46’ N, 21°32’ E. Its crew consisted of pilot Lt. Oskar Fuhrmann, observer Flg. Heinz Rietzsch, Onboard mechanic Ofw. Franz Bußkamp and gunner Fw. Max Muchowski. All four were KIA. 3./MSGr.1 ended the month of June with 24 aircraft. Four more Ju 52s were lost through enemy action in July. Three losses occurred on July 4th, when three pilots, 1st Lt. Walther J. Carroll Jr., Capt. Richard M. Gangel and 1st Lt. Arthur W. Kidder Jr., all of the 96th FS, 82nd FG each claimed a Ju 52 with a ring device shot down north west of Craiova, Romania. The losses were however made up and the strength of the unit remained 24 aircraft. August brought one loss due to enemy fighters, which was replaced. The only recorded loss of this unit for August, however, was due to a mine explosion. It occurred on 4 August and three men on board the aircraft died. On 25 August 3. Staffel of MSGr. 1 moved to Belgrade from Rumania. September 1944 was a disaster for the unit as 10 Ju 52/3ms were lost due to enemy action, with three more in October. The only loss we could identify occurred on 5 October, when a Ju-52/3m MS was lost at Dunaremete at km 1826 at 16:04 hours. Again, the cause was a mine explosion. The four crew were killed (pilot Ofhr. Karl Matula, radio operator Uffz. Willi Hendler, mechanic Fw. Hermann Fritsch and gunner Uffz. Franz Dreßler).
At the end of the month the unit had only eight serviceable Junkers. A Slovakian police report dated 6 October describes one of the last Ju 52 sweeps for Brtish mines in the Danube. Police officer Černý reported that since 14:20 hours every half an hour two German planes were flying low over the river up and downstream, and were fitted with big rings under the fuselage.
Text and photos based on the book “ Gardening by Moonlight” – 205 Group RAF mining operations over the River Danube in 1944, published in 2016 by Peter Kaššák and David Gunby (David is a son of an airman, who was lost during a 'Gardening' operation over Danube). Click on the link to go to the Lulu.com 'print-on-demand' page
For more Peter Kassak posts on the Luftwaffe blog go here
Slovak Spectator article on British mines in the Danube during the summer of 2026