Up to the time of writing the Department of Construction has refused to divulge the characteristics of these three boats, and has confined itself to mentioning their cost and the name of the designers. It has been stated in some of the French service journals that Q 37 will be driven on the surface by an alcohol motor, and submerged by compressed air in place of accumulators. No submarine boats are to be laid down in France in 1902. In 1903, 13 will be laid down, and by the close of the year 37 are expected to be in commission. By the year 1906 France should be in possession of a submarine flotilla numbering 68 vessels. Q 38–42 and Q 61–68 are to be built at Toulon, Q 43–50 at Rochefort, and Q 51–60 at Cherbourg. Of these 31 boats it has been stated that 8 will be submersibles with a double motive power, _i.e._, a vapour or gas engine and electric accumulators. They are to have a radius of action a little more extended than that of the submarine proper, and will plunge more rapidly than the _Narval_ and _Sirène_, which have to fill the ballast tanks between the hulls. APPENDIX IV SUBMARINES OLD AND NEW To give some description, even of the briefest nature, of every submarine boat that has ever been constructed would necessitate a volume three or four times the size of the present work. There are, however, a few vessels that demand some notice here. [Sidenote: Payerne.] The first inventor to propose a mode of propulsion other than by hand-operated mechanism, was Dr. Payerne, who in the fifties proposed a boat which was propelled by a screw driven by a steam engine, furnished with two boilers, an ordinary boiler-furnished steam for surface navigation; whilst the other, which he termed a “chaudière pyrotechnique,” for use beneath the waves, was so arranged as to burn in hermetically closed furnaces a combustible containing in itself the oxygen necessary for its combustion. The products of combustion escaped by raising a plug so devised as to prevent water entering the fire-box. The combustibles to which Dr. Payerne gave preference were:— Coke 165 Nitrate of Soda 835 Coke 145 Nitrate of Potash 855 The boat was known by the name of _L’Hydrostat_; but, as its inventors were not able to work out their ideas satisfactorily, it was turned into an ordinary diving-bell, and used for submarine excavations at Cherbourg and at Brest. [Sidenote: Riou.] In 1861 Olivier Riou built two models, one driven by steam (generated by the heat of ether in combustion), and the other by electricity derived from batteries. This is the first occasion that we find electricity requisitioned for the propulsion of an under-water vessel. [Sidenote: Alstitt.]