1915] SUBMARINE Boats 131 
in case of emergency, even when the boat is at a great depth. The time 
occupied in passing from the surface to the submerged condition should 
be not more than about from 4 to 5 minutes. This, of course, is a point 
of great military importance. Since the main tanks are always filled 
completely when it is desired to dive, it is necessary to fit one or more 
auxiliary or regulating tanks of moderate capacity to allow for varia- 
tions in the specific gravity of the water and for changes in the weight of 
the boat due to consumption of provision, stores, etc. The consumption 
of fuel-oil is roughly compensated for by admitting water to the bottom 
of the oil tanks, which are thus always kept completely filled. The 
buoyancy of the boat in the submerged condition is so adjusted that a 
small “‘reserve buoyancy”’ remains, leaving always a tendency to rise 
to the surface. This tendency is overcome dynamically when the boat 
is in motion either by hydroplanes or by giving the boat a slight down- 
ward inclination by the head. 
Small tanks, one at each end of the boat, permit an accurate adjust- 
ment of the trim (the longitudinal balance). Special tanks are fitted 
for compensating for such losses in weight as when a torpedo is fired and 
another is inserted in the tube. In some boats a so-called “ floating 
tank”’ is fitted, connected with a continuously acting pump which is 
worked in conjunction with the horizontal rudders; this tank serves to 
compensate automatically for incidental variations in buoyancy occurring 
after the boat has got under way, notably those due to changes in 
the specific gravity of the water. A considerable amount of buoyancy 
can be obtained almost instantaneously in case of emergency by the 
release of the safety-keels referred to above. 
The superstructure which is above water in the light condition is 
self-bailing. In some boats it is entirely and permanently open, 
serving only to provide a raised platform, but in most boats it is a water- 
tight structure provided with large and numerous valves that can be 
readily closed when the boat is in light condition whereupon the super- 
structure will add to the reserve buoyancy and the stability. 
VENTILATION AND HABITABILITY. 
Space is always restricted in a submarine boat. When going on the 
surface the motor gives off much heat and requires a great amount 
of air for its combustion. It is unavoidable that some of the products 
of combustion, carbon monoxide and carbonic oxide, leak out from the 
engine. Also the men consume oxygen and produce carbonic oxide, 
and when charging the batteries free hydrogen is liable to be liberated, 
forming with the air in the boat an explosive mixture. Where the fuel 
is gasoline or other very volatile oil, it will evaporate at a low tempera- 
