THE CONQUEST OF TIME AND SPACE 



war purposes, have proved quite as practical as the 

 Hollands. In recent tests of these two types by the 

 United States Government the Holland boats showed 

 themselves to be slightly superior to the Lake boats in 

 certain particulars, but the margin of superiority was 

 a very narrow one. 



The boats of the *^ Octopus" type are strictly speak- 

 ing "diving boats," while the Lake boats are of the 

 "even-keel" type. These terms refer to the method 

 of submergence, the diving boats changing their hori- 

 zontal trim when submerging, while the even-keel 

 boats retain their horizontal trim, or nearly so. 



The Lake boats have some features not usually em- 

 bodied in other submarines, since some of the boats 

 are designed for purposes other than warfare. Thus, 

 they are equipped with wheels, or buffers, on which 

 they can roll along the bottom of the ocean or bay. In 

 the bow is an air-tight compartment with an opening 

 in the bottom through which a diver can emerge and 

 work on wreckage, or laying and disconnecting mines. 

 These boats have also a safety device in the form of a 

 detachable keel weighing several tons. In case of acci- 

 dent, when it might otherwise be impossible to rise to 

 the surface, this keel can be detached simply by pull- 

 ing a lever, thus giving the boat sufficient buoyancy to 

 rise to the surface. This particular feature of the de- 

 tachable keel is not peculiar to the Lake boats alone, 

 some of the foreign submarines using a similar arrange- 

 ment as a safeguard. 



Technically speaking the name "submarine" is now 

 used only as applying to those boats that are operated 



[io8] 



