1915] SUBMARINE Boats 127 
II. A DiIscussION OF THE PRINCIPAL FEATURES OF THE DESIGN OF 
SUBMARINE BOaATs. 
SUBMARINES AND SUBMERSIBLES. 
The ‘submersible’ has already been defined as a submarine boat 
in which predominant importance is given to the requirements of service 
in the light condition, while the ‘“‘submarine”’ is designed more particu- 
larly with regard to the submerged condition. Hence the ship-shaped 
form of the submersible and the spindle-shaped form of the submarine. 
The external ship-shaped form of the submersible is however attained 
without abandoning the advantage of the circular section which is 
maintained throughout an inner spindle-shaped ‘“strength-hull”’, 
because it is the form best adapted to resist the pressures of the water. 
Between the inner and the outer shell are water-ballast tanks and oil 
tanks, whence the strength hull may be of small diameter well suited 
to resist great pressures without going to excessive scantlings. The 
outer hull, not being exposed to great pressures, may be lightly built 
and will yet in some measure protect the inner hull against damage by 
collision. At the same time the ballast and oil tanks may, with a rela- 
tively small addition in hull weight, be made very large, whence a great 
reserve buoyancy and great radius of action can be secured. In a sub- 
marine the tanks are chiefly inside the strength hull and cannot, cthere- 
fore, be very large without unduly increasing the diameter of the hull 
and hence its tendency to collapse. 
Speaking broadly, the submersible has better seagoing qualities 
and a higher speed on the surface than the submarine, but the form is 
not so favorable for driving under water. Most early boats were sub- 
marines. It was natural that inventors, especially those not acquainted 
with the requirements of naval service, should direct their efforts especi- 
ally to navigation under water and that they should underestimate 
the importance of qualities required for work on the surface. At present 
the general trend of the development is towards the submersible type. 
Of recent years, therefore, the submarine, where it is still retained, 
has approached more and more to the submersible by an enlargement of 
the superstructure, which at the same time has been given a more 
ship-shaped form. In English submarines side structures have been 
added. The reserve buoyancy in the early submarines was only about 
5 per cent. of the light displacement, but has been gradually increased 
to about 18 or 20 per cent. In submersibles, on the other hand, the 
reserve buoyancy has been reduced from about 72 per cent. in the Narval 
to about 35 per cent. or less in recent boats. 
