During the Second World War, Operation Clipper was an Allied offensive by the British XXX Corps (which included the American 84th Infantry Division) to reduce the Geilenkirchen salient in mid-November 1944. Clipper was the preliminary to a wider Allied operation, Operation Queen, to gain control of the Roer valley and of the Hürtgen Forest.

Geilenkirchen is situated on the Wurm River, some 20 km (12 mi) north of Aachen. The surrounding area is undulating, alternating between woodland, farmland and industrial villages. The area was crossed by a network of passable minor roads, some major roads and a railway line. The Wurm is the major geographic feature.

The salient was a German position on the Siegfried Line (Westwall) at the boundary between the British Second Army and the American 9th Army. It restricted the movement of Allied forces and was a potential threat.

Anglo-American cooperation was prompted by the availability of British artillery and the specialised armour support of "Hobart's Funnies" (such as flail and flamethrower tanks). A two-pronged attack was planned on the salient and the temporary attachment of the 84th Infantry Division to XXX Corps, avoided problems of divided command. The British part of the operation was coordinated from 13 November to 24 November in a house at Laurastraat 67 in Eygelshoven (now Kerkrade).

The operation was planned to take four phases. First, on 18 November the U.S. 84th Division – commanded by Major General Alexander R. Bolling – would pass through the troops manning the frontline, advance north-east 2 mi (3.2 km) and take Prummern and the surrounding high ground, east of Geilenkirchen. Second, at midday, the British 43rd (Wessex) Infantry Division – commanded by Major-General Ivor Thomas – was to advance and capture the high ground north and west of the town (around Bauchem and Tripsrath). Once done, Geilenkirchen would be virtually encircled, and the 84th Division would occupy the town and its north-eastern suburbs (third phase) before, in the fourth phase, both divisions would advance north-east about 3 mi (4.8 km), clearing both sides of the Wurm. The final objectives were the villages of Hoven, Müllendorf, Würm and Beeck.

For aerial support the operation had aircraft from RAF Second Tactical Air Force and the XXIX Tactical Air Command.^{[citation needed]}

The German defenders consisted of the bulk of the 176th Infantry Division, northwest of Geilenkirchen, and the extemporised 183rd Volksgrenadier Division, in the town and southeast of it. General der Infantrie Günther Blumentritt—commander of the XII SS Corps which the 176th and 183rd were subordinate to —had placed the bulk of his artillery in the area.

South-east of Geilenkirchen, deep minefields had been laid from Geilenkirchen to Jülich, via Immendorf and Puffendorf, about 10 km (6.2 mi). The area was at the point where a new section of the Westwall, built while Aachen held out, joined the established defences. Westwall used the compact, stone-built buildings in the villages, which had been fortified, and purpose-built concrete bunkers.