There are some destructive actions in connection with large, high-speed, light-weight internal-combustion engines which practically all designing engineers have failed to grasp. Otherwise, engineers of all nationalities would not have failed to the extent they have; and I do not believe that there is a submarine engine in service to-day which has fully met the expectations of its designers and builders. It is unfortunate for the engineering profession that government policy will not permit of a full disclosure of the defects of engines and other equipment in government-owned vessels. Were a frank disclosure made, other inventors and engineers would, in all probability, take up the problems and they might the sooner be solved. All the earlier submarines were equipped with engines which used gasolene (petrol) as a fuel, but the gas from this fuel, when mixed with a proper proportion of air, is highly explosive. A number of serious explosions occurred in submarines due to this gas escaping from leaky tanks, pipings, or valves. Some of them were accompanied by loss of life. The most disastrous was that on board the Italian submarine _Foca_, in which it is reported that twenty-three men were killed. Therefore, several years ago, all governments demanded the installation of engines using a non-explosive fuel; and builders then turned to the "Diesel" engine as offering a solution of the problem. As early as 1905 I had anticipated that such a demand would ultimately be made, so during that year I built, in Berlin, Germany, an experimental double-acting heavy-oil engine; but unfortunately the engineer in charge of the work was taken ill and eventually died. This engine was later completed and showed great flexibility in its control and in reversing. It, however, has never been put on a manufacturing basis. In the meantime, others took up the work of developing the heavy oil Diesel engine for submarines. The first of the Diesel type engines to be installed in a submarine were built by a well-known French firm of engine builders. As we were then in the market for heavy-oil submarine engines, plans of these engines were submitted to me, but I found it impossible to install them in any boat we then had under construction, owing to their size and weight. I have been advised that engines of this design were installed in some of the French submarine boats. I have also been informed that the shock and vibrations produced by them were such as to cause the rivets in the boats to loosen, and this started the vessels to leaking so badly that it was found necessary to take them out. These engines differed only slightly from the vertical Diesel land engine. The engine is the most important element in the submarine. Without this it is impossible to make long surface runs, and in the event of its disablement it is impossible to charge the storage batteries to enable the submarine to function submerged, which is, of course, what she is built for doing.