1915] SUBMARINE Boats 125 
experimenters who held that the axis of the boat should as far as possible 
be kept horizontal, Holland boldly effected immersion and emersion 
by ‘‘porpoising’’, 7.¢., by inclining the axis, sometimes to great angles, 
using the horizontal rudder fitted in the stern. This method of con- 
trolling the vertical motion proved satisfactory although not without 
danger, for it has happened that boats of the Holland type took deep 
involuntary dives. Holland’s experiments showed the great importance 
of keeping the centre of gravity immovable and of compensating for 
all changes in buoyancy. 
The Holland type was reproduced in the United States Navy in 
the Adder Class and following types and in England Vickers commenced 
building the A-class for the British Navy. 
During the “‘nineties’’ another American Mr. Simon Lake constructed 
several experimental boats, and evolved a type of which the Protector, 
t#its., built in 1901-2, was the first representative. 
The Protector belongs to the submersible type, having a ship-shaped 
superstructure and a reserve buoyancy in the light condition of about 
28 per cent. of the light displacement. Diving and emersion takes 
place as in the Gustave Zédé by four horizontal rudders, the boat being 
always kept nearly on even keel. Mr. Lake’s first idea was to produce 
a boat suitable for salvage operations and the like, and he for this pur- 
pose fitted wheels forward and aft hung by pivoted steel jaws fitted 
in pockets in the bottom and cushioned by hydraulic cylinders. These 
wheels enabled the boat to run along on an even bottom with a slight 
deficiency in buoyancy. The means of propulsion are the same as in 
the Holland. 
MODERN BOATS. 
The early development of submarine boats was groping and 
erratic, the “eighties” and “‘nineties’’ was a period of experimentation, 
resulting in a great variety of types, but after about the year 1900 boats 
entered into actual military service, with the result that an elimination 
of the less practicable features took place, and there followed a move- 
ment towards a unification of type. At the same time the nautical and 
military requirements led to a steady increase in displacement and 
power. Great progress was made in perfecting the various technical 
appliances. We shall now briefly describe recent types of boats so far 
as their various features have been made public. 
In the British Navy the Holland type was gradually modified con- 
siderably. The ratio of length to diameter, which in the A-class was about 
54%, was much increased. Later boats were given large side structures 
patched on outside the spindle-shaped strength hull, the object being 
