Sperrbrecher M 32 Mur

Again a bigger scratch 1/300 project, a Sperrbrecher.

The Sperrbrecher was not unique to Kriegsmarine but no other navy used them in such extent. The birth year was 1903. A commission under Vizeadmiral von Tirpitz was ordered to present ideas to protect the Hochseeflotte from sea mines.

The report includes the first naming of Sperrbrecher. Naval dictionaries translate it with barrier breaking vessel but most English books just use Sperrbrecher because that ship type is seen to be as German as Kindergarten.

The idea was simple. A merchant vessel would steam in front of the battleships and explode the mines. It was to be filled with sand ballast, fascines and a large number of casks to keep it afloat. In WW I devices got developed to protect the bow. Cutting the cables of mines and getting them away from hull contact was the only protection in WW I. Not all worked well.

Other towed devices added size to the cleared way, up to some 50 meter and 20 m depth.
In 1918 the RN started to use magnetic mines without much effect. At armistice no clearing device was ready.

WW II Sperrbrecher started with little alterations in 1939. The bow protection was now the Otter device. In the 30’s towed cables are developed to fight magnetic mines. These reacted on the metal ship’s magnetic field and so a towing vessel would be blown up if it ran over a mine. RN developed the degaussing to reduce the field. That worked well, but the wiping had to be done again and again because the ship’s field came back. And the later fuses reacted on wiped hull too.

1940 saw the only larger use of Sperrbrecher type vessels by RN, the Mine Destructor Vessels. 10 got converted but sooon used as ordinary merchants.
Kriegsmarine met the first British magnetic mines at the end of 1939 and soon the VES Sperrbrecher became the answer. Voraus Eigen Schutz was a gigantic electric magnet. A copper cable was slung behind the bow around the hull some 100 times. Up to 6000 meter! Inside was an iron core of up to 2000 tons!

It produced a very strong field that exploded the 140 mines some 100 meter before the Sperrbrecher. RN reacted with an anti Sperrberecher mine with a very blunt fuze that only reacted to a super strong field. Exploding under the Sperrbreche. Kriegsmarine countered that with the Umpolvorrichtung that changed the poles every 10 seconds.

Another special fuse was activated by a strong field but not exploded. Only a smaller following it exploded it, normally caused by an escorted vessel. A similar combined a magnetic sharpening with an acoustic impulse in the next 15 minutes.
Germans and Allies used Acoustic mines and Sperrbrecher had to get devices to counter them by producing sounds in front of vessel.

And the Kriegsmarine developed pressure-activated mines that had been much harder to counter.
To tell about the myriad of changes in fuses and counter measures would fill a book.

The Sperrbrecher had high losses. Some 50 % are lost in action, many by mines but late war more to air attacks. To counter that the Flak was much increased. The small German convoys benefitted from that.

The typical formation was with the VES Sperrbrecher in front, 300 meter before next ship. The magnetic field would damage compass and other sensible stuff. Two M boats abreast followed, mine searching and giving AA cover. Then the escorted vessels followed. In most convoys one to five vessels. And behind them the bigger escorts (Zerstörer, Torpedobbote or more Minensucher) followed in a line.