The Hohenzollern Redoubt action, 2–18 March 1916 was fought on the Western Front during the First World War. The Hohenzollern Redoubt was a German defensive position north of Loos-en-Gohelle (Loos), a mining town north-west of Lens in France. The Redoubt was fought over by the British and German armies from the Battle of Loos (25 September – 8 October 1915) to the beginning of the Battle of the Somme on 1 July 1916. Over the winter of 1915–1916, the 170th Tunnelling Company RE dug several galleries under the German lines in the area of the redoubt, that had changed hands several times since September 1915. In March 1916, the west side was held by the British and the east side was occupied by the Germans, with the front near a new German trench known as The Chord. No man's land had become a crater field and the Germans had an unobstructed view of the British positions from the slag heap. The British front line was held by outposts to reduce the number of troops vulnerable to mine explosions and the strain of knowing that the ground could erupt at any moment.
The 12th (Eastern) Division was selected to conduct an attack to capture the crater field, gain observation from crater lips over the German defences back to and end the threat of German mine attacks. Four mines, the largest yet sprung by the British, were detonated on 2 March and followed up by two battalions of infantry, which captured the new craters, several German occupied craters, Triangle Crater which had not been seen until it was overrun and a large length of The Chord, most of the rest being obliterated in the explosions. The main entrance of the German mine galleries was discovered in Triangle Crater and the 170th Tunnelling Company RE crossed no man's land to demolish the entrance. German counter-attacks concentrated on the recovery of Triangle Crater, which was re-captured on 4 March. The recovery by the Germans of the gallery entrance threatened the positions captured by the British, who attacked Triangle Crater on 6 March and were repulsed.
The British tunnellers got into the German gallery system from a British tunnel and were able to demolish the system on 12 March, which relieved the threat of another German mine attack. Skirmishing around the craters diminished and it was thought that the Germans were concentrating on consolidating new positions. On 18 March, the Germans surprised the British with five mines which had been quietly dug through the clay layer above the chalk. The German attack had nearly as much success as that of the British on 2 March, forcing them back to the original front line, before local counter-attacks regained some of the craters. When the fighting died down after 19 March, both sides occupied the near lips of the craters. Brigadier-General Albemarle Cator, the 37th Brigade commander, recommended that attempts to occupy craters should end and the near lips be held instead, because craters were death traps against howitzer and mortar fire; observation from the crater lip was obstructed by its convex shape and the large lumps of chalk brought to the surface by the explosions.
Background
Mining 170th Tunnelling Company began work for a mining attack on the Hohenzollern Redoubt on 14 December 1915. By the end of the month, it was in the process of sinking six shafts. Two sections of 180th Tunnelling Company were then attached to 170th Tunnelling Company, and the miners began another three shafts. Mining was carried out in the clay layer to distract the Germans from other mine workings in the chalk. In the meantime, the Redoubt area had changed hands several times since September 1915. In March 1916, the west side was held by the British and the east side was occupied by the Germans, with the front near a new German trench known as The Chord. The Germans had an unobstructed view of the British positions, from a slag heap called and in previous mining operations no man's land had become a crater field. The British front line was held by outposts, to reduce the number of troops vulnerable to mine explosions and the strain of knowing that the ground could erupt at any moment. It had been calculated that the German mining effort in the area of the Redoubt was six weeks more advanced than the British effort.
Mining was intended to destroy fortifications and the troops in them and to prevent the opponent from doing the same. Mining had to be conducted under conditions, which concealed the effort from the opponents, to prevent counter-mining. Excavated material in the Loos area was chalk and thus easily seen; some of the material was used in the front line but most had to be removed by large carrying-parties and dumped out of sight of German ground observers and the crews and cameras of reconnaissance aircraft. A shaft was dug well back in the defensive system and then a gallery was driven forward, with branch galleries dug at intervals. As the main gallery got close to German defences, the need for silence became paramount, to elude the Germans conducting a similar mining operation. Plans of the mine workings were kept, on which rival German works were plotted, based on mines already sprung and the reports of listeners.
When galleries came close, a (a small mine insufficient to disturb the surface) would be planted, to collapse the opponents' gallery and then the digging of the offensive gallery would resume. If the gallery reached the target, a chamber would be dug and then loaded with explosives, ready to fire. The nearing of a German gallery, listening for clues, breaking into a rival gallery and waiting for the mine to explode, caused great strain to the miners and was nerve-racking for troops in front line positions on the surface, who knew that a mine could be sprung under them at any moment. To reduce the danger to front-line troops, the area was held by posts rather than a continuous front line, with only the minimum number of troops. German mining had formed craters in no man's land, named craters the British and which were held by each side, dug in on their respective near lips. In February 1916, mining was being conducted at the Quarries and near , where explosions were frequent and were followed by infantry attacks to occupy the near lip and by sapping forward.
Prelude British offensive preparations The British effort over the winter gradually overtook the German mining operation and a plan was made to destroy the German galleries. Four mines were planted under the Redoubt, to be exploded just before an attack on The Chord, which would leave the British in possession of the crater-field, counter the German advantage in observation from and possibly lead to the destruction of the German gallery system. Chamber A was loaded with of ammonal, Chamber B with of blastine and of ammonal; Chamber C was loaded with a charge of , the Germans being apparently taken unawares. While the 36th Brigade was out of the line resting and training, the 37th Brigade conducted preparatory work, dumping hand grenades close to the front line, preparing communication trenches, jumping-off places and arranging to carry hot soup to the raiding parties after the attack.
British plan of attack The commander of the 170th Tunnelling Company produced a forecast of the effect of the mines, to help orientate the attackers, in which mines A and B were predicted to make craters wide, deep and that Crater C to be wide and deep. The fourth, smaller mine had been planted under the side of Crater 2 and was expected to leave a bigger crater, slightly offset. The 12th divisional artillery was supported by the 59th and 81st Siege batteries and the I Corps artillery supplied a section of 9.2-inch howitzers, two sections of 8-inch howitzers and two sections of 60-pounder guns. No preparatory bombardment was to be fired but from ten trench mortars were to fire on Crater 1 and The Chord; as the attack began, the mortars were to fire smoke to screen the advance. As a precaution, the front line infantry were to be withdrawn, before the mines were sprung.
German defensive preparations Increased British activity at the end of February near the Redoubt, an unusual amount of patrolling and greater amounts of heavy artillery and trench mortar fire, put the Germans on their guard against a British attack. The area was held by I Battalion, Bavarian Infantry Regiment 23 and III Battalion, Bavarian Infantry Regiment 18 of the 3rd Bavarian Division, each with three companies in the front line and one in reserve.
Battle
2 March
At three mines were sprung, about short of The Chord, which made crater lips from which the German trenches could be seen. As dark fell, the 9th Royal Fusiliers (9th RF) attacked on the right, as the 8th Royal Fusiliers on the left and troops of the 35th Brigade on the right, gave covering fire. There had been much snow, sleet and rain during the week previous and the attackers found that in the displaced earth from the mine explosions, they were shin deep. C Company of the 9th RF reached craters 1, 2 and A, then stumbled on Triangle Crater with few casualties. A party detailed to block Big Willie Trench ran down the south-east face of the crater, caught the German trench garrisons in their underground shelters and took before being slowly driven back to Triangle Crater, after they ran out of hand grenades. Fifty men assembled on the western face, where they were showered with debris from mine A; twenty men were temporarily buried. The rest of the party captured The Chord, from crater A to C4 Trench and then repulsed German counter-attacks.
On the left flank, the 8th RF captured craters 4, B and C but the party that attacked to capture The Chord from B to C4 were caught in no man's land by the Germans; only two men reached the objective. Twenty men from a supporting unit joined the two survivors but The Chord had mostly been destroyed in the area, leaving little cover. The British eventually fell back to the crater line, where another twenty men arrived and helped to hold the position and consolidate craters 4, B and C. German counter-attacks were made all through the night but were repulsed and consolidation was begun, despite the loss of contact with the rear and the soft ground. The 170th Tunnelling Company followed up the infantry and began to blow up the German gallery entrance found in Triangle Crater. The objectives of the attack had been achieved, except at the north end of The Chord and a later bombing attack up The Chord from the south by the 9th RF, was also repulsed.
3–5 March At the 36th Brigade commander, Brigadier-General L. B. Boyd-Moss reported that the situation was satisfactory, the craters having been captured, consolidation begun and the unexpected Triangle Crater had been captured, in which had been found the main entrance of the German gallery system. Observation of the German lines back to had been gained, some of The Chord had been captured and much of the rest had been destroyed but German artillery-fire from had caused many casualties. During the day, the two attacking battalions were relieved by the 11th Middlesex and the 7th Royal Sussex (7th RS) battalions. Immediate German counter-attacks failed until 4 March, when an attack at from The Chord and Little Willie Trench was repulsed. More attacks at were driven off, then at another German bombardment began on the craters on the right flank and Triangle Crater was recaptured by three attacks.