ABSTRACT The objective of this study is the conceptual design of a device which could be used to exothermically weld a stud, bar, or a padeye to underwater structures. The process is commonly called thermit welding. Several problem areas involved in underwater thermit welding are considered. A theoretical temperature simulation model is developed and verified experimentally. The effects of wetness on weld strength and ability of the thermit process to weld on a "dirty" surface are investigated experimentally. A conceptual design is prepared on the basis of experimental results. INTRODUCTION Man's capability to work in the ocean environment has increased dramatically. This increase capability has created a need for cutting and joining techniques which can be applied in the underwater environment. Today, most of underwater joining and cutting operations are done by use of metal arcs and oxyacetylene torches. However, operations using a diver, today and for the foreseeable future, appears limited to depths of less than 1000 feet, even employing recent developments in saturated diving. Currently, there is no method for joining metals in water deeper than a diver can reach. Man's deep sea capability could be greatly expanded if a technology for joining metals in deep sea could be developed. Considering the fact that about 95 percent of the entire ocean floor is deeper than 1000 feet, there is a strong need for developing a capability for welding in deep sea, particularly for salvage work. One way to perform the welding work is to use a deep submersible, and employ a welding process which can be controlled remotely. The use of an exothermic welding process (thermit) may offer a possible solution because the process has the following unique characteristics. It requires no power supplies. A complete, watertight package could be developed which can be ignited at any time by remote control. As long as the device is properly designed, virtually no welding skill is require to ignite it. (It is worthy of mentioning that the G. C. Marshall Space Flight Center, NASA, plans to conduct exothermic brazing experiments in outer space in the Skylab project (1). Compact and reliable exothermic brazing units have already been developed for NASA). The possible value of such a device has been recognized by the Navy personnel engaged in salvaging work. As a result, toward the end of 1970, the Office of the Navy Supervisor of Diving, Salvage, and Ocean Engineering, Naval Ship Systems Command, granted funds to the Massachusetts Institute of Technology to investigate characteristics of the thermit reaction in the underwater environment and its applicability to the remote-controlled welding of a 50-ton padeye to underwater structures.