SUBMARINE NAVIGATION 269 



constitutes what is technically called a ' reserve of buoyancy.' In the 

 submersible this reserve of buoyancy and the accompanying freeboard 

 is greater than in the submarine type, and in this respect lies the chief 

 difference between the two types. The submersible has higher free- 

 board and greater reserve of buoyancy, which secure better seagoing 

 qualities, and greater habitability. The deck or platform is situated 

 higher above water, and to it the crew can find access in ordinary 

 weather when making passages, and obtain exercise and fresh air. Re- 

 cent exhaustive trials in France are reported to have established the 

 great superiority of the submersible type when the service contemplated 

 may involve sea passages of considerable length. The French policy, 

 as recently announced, contemplates the construction of submersibles of 

 about 400 tons displacement for such extended services, and proposes to 

 restrict the use of submarines to coast and harbor defence for which 

 vessels of about 100 tons displacement are to be employed. All recent 

 British submarines would be ranked as submersibles according to the 

 French classification, and it is satisfactory to know, as the result of 

 French experiments, that our policy of construction proves to have dis- 

 tinct advantages. In addition to these two types of diving or submarine 

 vessels, the French are once more discussing plans which have been 

 repeatedly put forward and practically applied by M. Goubet, namely, 

 the construction of small portable submarine vessels which could be 

 lifted on board large ships and transported to any desired scene of 

 operations. In the Royal Navy for many years past, it has been the 

 practise to similarly lift and carry second-class torpedo or vedette 

 boats about 20 tons in weight. Lifting appliances for dealing with 

 these heavy boats have been designed and fitted in all our large cruisers 

 and in battleships, and a few ships have been built as ' boatcarriers/ 

 The first of these special depot ships in the royal navy was the Vulcan 

 ordered in 1887-8, the design being in essentials that prepared by the 

 writer at Elswick in 1883. The French have also built a special vessel 

 named the Foudre which has been adapted for transporting small sub- 

 marines to Saigon, and performed the service without difficulty. 

 Whether this development of small portable submarines will take effect 

 or not remains at present an open question, but there will be no me- 

 chanical difficulty either in the production of the vessels themselves or 

 in the means for lifting and carrying them. M. Goubet worked out 

 with complete success designs for vessels about 26 feet long and less 

 than 10 tons displacement, with speeds of 5 to 6 knots, the trials of 

 which have been very fully described, but French authorities have not 

 adopted the type, and no decision seems to have been taken to intro- 

 duce it. In this country no similar action has been taken, and our 

 smallest submarines weighing 120 tons cannot be regarded as ' portable/ 

 Indeed, some leading British authorities on submarines have indicated 

 that experience is adverse to the construction of vessels in which not 



