'Clipper' was a British offensive by Lieutenant General B. G. Horrocks’s XXX Corps of Lieutenant General Sir Miles Dempsey’s 2^nd Army to eliminate the Geilenkirchen salient held by General Alfred Schlemm’s 1^st Fallschirmarmee of Generaloberst Kurt Student’s Heeresgruppe 'H' and jutting to the west of the Roer river at the junction of Field Marshal Sir Bernard Montgomery’s Allied 21^st Army Group and General Omar N. Bradley’s US 12^th Army Group (18/23 November 1944).

In a wider context, 'Clipper' was part of the larger US 'Queen' undertaking to gain control of the Roer river valley and the Hürtgenwald. Located on the Wurm river, Geilenkirchen is some 12.5 miles (20 km) to the north of Aachen in a region of rolling terrain containing woodland, farmland and industrial villages. Late in 1944, the area was crossed by a network of passable minor roads, some major roads and a railway line, and the Wurm river is the major geographic feature of the area.

The Geilenkirchen salient was part of Germany’s 'Siegfried-Linie' defences on the boundary between the 2^nd Army and Lieutenant General William H. Simpson’s US 9^th Army. Anglo-US co-operation was prompted by the availability of British artillery and specialised armour (such as flail mine-clearing and flame-throwing tanks), and the temporary attachment of Major General Alexander R. Bolling’s US 84^th Division to the XXX Corps avoided problems of divided command. A two-pronged attack was planned for the destruction of the salient, and the operation was schemed in four phases. Firstly, on 18 November, the 84^th Division would pass through the troops holding the front line, advance 2 miles (3.2 km) to the north-east and take Prummern and the surrounding high ground to the east of Geilenkirchen. Secondly, at 12.00 on the same morning Major General G. I. Thomas’s British 43^rd Division would advance and capture the high ground to the north and west of the town around Bauchem and Tripsrath. Geilenkirchen would thus be virtually encircled and the 84^th Division would occupy the town and its north-eastern suburbs in the third phase before, in the fourth phase, both divisions would advance about 3 miles (4.8 km) to the north-east and clear the area on each side of the Wurm river. The final objectives were the villages of Hoven, Müllendorf, Würm and Beeck.

The defence by General Günther Blumentritt’s XII SS Corps was based on the bulk of Generalleutnant Berthold Stumm’s 176^th Division (three grenadier regiments) to the north-west of Geilenkirchen, and Generalleutnant Wolfgang Lange’s 183^rd Volksgrenadierdivision (three Volksgrenadier regiments) both in and to the south-east of the town. Commanding the XII SS Corps in General Hasso-Eccard Freiherr von Manteuffel’s 5^th Panzerarmee in Generalfeldmarschall Walter Model’s Heeresgruppe 'B', Blumentritt had placed the bulk of his artillery in the area. To the south-east of Geilenkirchen, thick minefields had been laid as far as Jülich via Immendorf and Puffendorf, a distance of some 6.2 miles (10 km). The area lay at the point at which a new section of the 'Westwall', built while Aachen held out, joined the established defences.

At 06.00 on 18 November, and thus before the break of this winter day, the searchlights of the 357^th Searchlight Battery, Royal Artillery, provided 'artificial moonlight' (searchlights shining on the underside of the clouds) as hazy indirect illumination for the flail tanks supporting the infantry. These tanks moved toward the German minefield between Geilenkirchen and Immendorf. On the wet ground, mud lessened the efficiency of the flails, and combat engineers followed with mine detectors.

After a brief artillery bombardment, the US 334^th Infantry advanced through the cleared strips at 07.00 and easily secured the high ground to the east of Geilenkirchen. The right flank gave some concern to US commanders as a counterattack was expected and fresh German troops appeared to be present in the area, so the advance on Prummern was delayed until the flank had been secured. When the attack resumed, supported by British Sherman medium tanks, there was steady progress and the regiment had reached its objectives by a time late in the afternoon.

The British attack to the north and west of the town also achieved its objectives by nightfall. The Worcestershire Regiment advanced on Tripsrath, capturing its intermediate objectives of Rischden and intervening woods with little opposition and few casualties.

The preparatory artillery bombardment had effectively destroyed the morale of the German defenders, and rain had exposed much of the minefields. However, the rain also made it difficult to bring up armoured support, anti-tank artillery and supplies. An unsupported British advance on a copse, using Universal Carriers, was engaged by two German self-propelled guns and driven back with heavy losses. Despite further counterattacks and a number of 'friendly fire' casualties, the men of the Worcestershire Regiment occupied Tripsrath after dark with the support of the artillery, and held most of the village, sometimes with Germans as next-door neighbours.

Given the overall success of this first day’s fighting, Horrocks directed that the third and fourth phases should be combined on 19 November. To facilitate this speeding of the schedule, the 84^th Division continued its advance toward Süggerath rather than consolidating. A reconnaissance patrol toward Beeck, however, reported an impending German counterattack on Prummern by two companies of the 10^th Panzergrenadierregiment of Generalleutnant Harald Freiherr von Elverfeldt’s 9^th Panzerdivision, with six tanks. The night attack was driven back, but the US progress toward Beeck was delayed until just before dawn on 19 November. Resistance in Prummern continued until the following day, when the village was cleared with the support of British 'Crocodile' flamethrower tanks: the adjacent high ground, 'Mahogany Hill', which had held out for two days, was captured by a surprise US attack on 22 November.

On 19 November the Worcestershire Regiment had received neither supply nor support as there was no usable supply route, but fought off a counterattack by the 104^th Panzergrenadierregiment of Oberst Hans-Joachim Deckert’s 15^th Panzergrenadierdivision. Five Sherman tanks of the 4^th/7^th Royal Dragoon Guards, equipped for traversing mud, then arrived but almost immediately lost four of their number to artillery fire and a Panzerfaust anti-tank rocket-launcher. A second German attack, on Rischden, supported by two PzKpfw VI Tiger heavy tanks and two self-propelled guns, was engaged by anti-tank guns and tanks, as well as by flanking fire from Tripsrath, and driven back.

Events in the Prummern area had made the US commanders cautious, particularly as there was now a gap in the US line between the 84^th Division and Major General Ernest N. Harmon’s US 2^nd Armored Division some 1.5 miles (2.4 km) distant at Apweiler. This gap was plugged by the temporary attachment of the 405^th Infantry.

Geilenkirchen itself was subdued relatively easily by the 333^rd Infantry on 19 November, but the Allied advance suffered from the lack of support by the artillery, which had been held back by the fear of 'friendly fire' incidents, as had occurred earlier in the British sector. Two troops of British tanks from the Sherwood Rangers Yeomanry provided close support, but could not make up entirely for lack of artillery.

From Geilenkirchen, the advance continued to the north-east along the Wurm toward Süggerath. 'Crocodile' flame-thrower tanks subdued the increasing German resistance, especially the pair of pillboxes guarding the road into Süggerath. The capture of Geilenkirchen opened a supply route to Tripsrath, and while the German artillery bombarded Tripsrath for the next four days, the British infantrymen, sheltering in basements, suffered few losses.

The leading battalion of the 333^rd Infantry passed through Süggerath, bypassing determined German strongpoints and, strengthened by the arrival of a fresh battalion, cleared Süggerath during the night of 19/20 November. The 333^rd Infantry was still more than 1 mile (1.6 km) distant from the Wurm river, its final objective, but there was the possibility of establishing a coherent front line with the XXX Corps on its left and the 334^th Infantry on its right.

Then the weather intervened: intermittent showers were followed by a downpour on 21 November, turning the fields into mud-baths that rendered the tanks both ineffective and vulnerable.

The direct road to the Wurm river was mined and an alternative side road was blocked by debris and could not be cleared until a bulldozer could be brought up. The US infantrymen attempted to advance but, without tank support, were beaten back. When the British 'Crocodile' tanks were able to advance and assault the defences, there was rapid progress, many of the German defenders surrendering. The mud intervened again, however, bogging down the armoured but wheeled trailers which carried the fuel for the flame projectors of the 'Crocodile' tanks. Without their support, infantry attacks on Müllendorf failed, particularly as the German defences had been strengthened by the advent of the 15^th Panzergrenadierdivision.

A flanking attack by the 405^th Infantry toward Beeck on 22 November also became bogged down against prepared defences. British assaults, on the other side of the Wurm river, were also beaten off by strengthened resistance. Despite the frustrations of 21 and 22 November, and the failure to capture the final objectives, the purpose of the operation had now been achieved at an Allied cost including 2,000 US casualties including 169 killed, 752 missing and 500 to non-battle factors.

The Geilenkirchen salient had thus been effectively removed and Major General Alvan C. Gillem’s US XIII Corps of the 9^th Army now had room to manoeuvre. The 84^th Division then reverted to US control and further attacks were abandoned on 23 November.