Abstract: Disclosed is an apparatus for simultaneously trenching and laying a submarine pipeline within the bed of a body of water covered with a relatively thick ice mass. The apparatus comprises a pipeline construction spread which precedes a trenching and pipe installation spread, both of which traverse the ice mass. The pipe installation vehicle advances toward the constructed pipeline, elevates the pipeline, forms a slot-like opening in the ice and directs the pipeline into the water through the slot. A submersible dredging assembly extends from a installation vehicle which forms part of the installation spread. As the vehicle advances, the dredging assembly forms a trench in the sea bed. At the same time the dredging assembly guides the pipeline into the trench and provides support to a submerged component of the pipeline which is threaded through a slot in the dredging assembly.