Abstract: The plough has a front and a rear lifting assembly (60, 62) each including an arm (64, 80) which is extensible and angularly adjustable by hydraulic rams (65, 68; 81, 84). The arms carry rollers (74, 76, 78; 94, 96, 98) upon which the pipeline (110) is lifted by the arms. The plough can be positioned beneath the pipeline as the arms retract while supporting the pipeline as the plough approaches the pipeline from one side. Having been positioned, the plough advances to cut a trench, the pipeline being supported in yielding manner by the two arms, having their lifting rams (68, 84) connected to hydraulic accumulators. Pressurized gas in the accumulators maintains the rollers (74, 76; 94, 96) in contact with the pipeline as the plough moves up and down and pitches relatively to the pipeline, during ploughing. The plough requires no structure over the pipeline. The plough body (12) is not required to comprise parts which separate to allow positioning of the plough in relation to the pipeline.