ABSTRACT This paper describes a new concept for the repair or connection of large diameter submarine pipelines beyond the practical working depth of divers. A repair/connection tool system is incorporated into an unmanned controlled buoyancy vehicle, powered through an umbilical cable from a surface vessel selected for local sea conditions. The need for heavy Lift capability is eliminated since the vehicle rests on bottom while working. Repair is accomplished by replacing a sectional pipeline with a new section including articulating means for accommodating misalignment of the damaged pipe cut ends) and mechanical couplings having longitudinal adjustment capacity. INTRODUCTION In the near future, submarine pipelines laid in water depths beyond the practical working depth of divers will become a reality. The offshore oil industry is in a period of accelerating growth. A large percentage of the remaining undiscovered-red petroleum reserves are believed to be beneath the waters of the continental shelves and slopes. This offshore expansion might be expected to continue into those ever deeper waters. Exploratory drilling has already moved into several thousands of feet of water in many areas. Several major programs have been announced for development of production equipment for the fields which, hopefully, are to be produced in these water depths. With production will come the need for flow lines, transfer lines, and trunk lines either to shallow water facilities or to shore. Much of the technology required to design and construct deepwater pipelines has already been developed. Many of the concepts have been verified in actual construction operations in today's water depths. The non-routine operations such as sea floor connections, general maintenance, or pipeline damage repair have not received the same attention. The forces of nature and the activities of man may expose any underwater structure to the risk of damage. In the case of the submarine pipeline, this damage might be expected to take one of the following forms: Minor deformation of pipe cross section Leak or failure due to pipe defect Leak due to corrosion Buckle or collapse of pipe Break or separation of pipe The risk of damage to the pipe during construction can be greatly reduced by improved design and construction methods that are now available. Pipe defects may be avoided or detected prior to installation by careful specification of pipe, backed by a program of supplemental non-destructive testing. Corrosion leaks may virtually be eliminated; as evidenced by experience with existing major offshore pipelines by the application of coatings, the use of sacrificial anodes, and. The complication of impressed current catholic protection. However, it may be assumed that any pipeline installed in an area of difficult seaflloor conditions, heavy-gear trawling, or marine construction will be exposed to the risk of damage. If it is also assumed that any lengthy interruption of service on a trunk line will result in shut-in production and/or interruption in supply to customers, the need for a method to minimize the downtime during repairs is obvious.