Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Although electric welding has been used for many years for repair work, there exists to-day a hesitancy in applying it to new construction, especially to the joining of heavy steel parts. It is the purpose of this book to endeavor to dispel this apprehension. The data of tests made in the spot welding of heavy steel plates by the Emergency Fleet Corporation is furnished in full with the expectation that in making this information avail able to shipbuilders and others, they will be able to adopt this process to their own manufacturing advantage. In like manner the underlying question of arc-welding proc esses is fully discussed with the intent of reassuring any one who may doubt the ability of these methods to supersede the rivet. The author wishes to acknowledge the courtesies ex tended to him both by those who have contributed to the text and those who have permitted the reprinting of valuable published material.