and firing mechanism in a separate bl10y called a " contact buoy ...

SUBMARINE MINES 401
in the harbor of Santiago, leaving the greater part of Admiral
Sampson's fleet free to engage in other operations. The subject
is one of growing interest and importance.
34. Plan of Mine Defense.-The plan of mine defense to be
adopted for any particular seaport can only be decided upon after a
careful study of the conditions peculiar to that port-the character
of the channels, the depth of the water, strength of currents, rise
and fall of the tide, etc. All these points having been carefully
noted, the positions of the mines, or groups of mines, are laid
down on the chart. As a general rule, ground and contact mines,
singly or in groups or lines, are placed in shoal water, the former
being preferred wherever the currents are strong. Groups of observation
mines, or electro-contact mines, are usually placed in
deep water and at outlying points, and the groups are so spaced
that a ship passing between the groups of one line will pass over
those of the line next inside. The mines are all numbered and a
table of angles is given to the officer who lays the mines, so that
they may be laid in accordance with the plan.
35. The Mine Field.-The whole space occupied by mines is
called the "mine field." It should be swept by the fire of small
guns to protect it from countermining operations, and by electric
searchlights to guard against night attacks upon the mine cables.
Plate III, Figs. I, 2, and 3, shows the general plan of a mine
field and the group formations used for observation and electrocontact
mines.
36. Spacing of Mines.-I£ the plan of the mine defense does
not contemplate that all the mines in one group, or line, are to be
fired simultaneously, it is evident that care must be used to plant
the mines at such intervals that the explosion of one may not
cause those adjoining it to explode, or even to signal in the case
of observation mines. It is not easy to give a rule for this distance,
but one authority states that mines containing 100 pounds
of gun-cotton should be spaced about 100 feet apart. The larger
the mines the less desirable will it be to fire more than one mine
at a time, and the greater must be the distance between them.
Mines containing 500 pounds of gun-cotton should be spaced about
320 ft. apart. For these reasons it is obviously wise to distribute
the mines over a wide area and in many different lines. The com-