Note.—In this latter instance, though the mines may not be covered by any guns, still they will be of great use, in so far, that being mechanical ones, they cannot be rendered useless by the process of cutting cables, etc., but must be destroyed, which in time of peace is a work of considerable labour and danger, and, therefore, would in the time of war, cause at the very least, serious delay to an enemy desirous of effecting a landing, etc., at a point so protected.
There are numerous objections against their employment, the principal ones being:—
1.—That they are all, more or less dangerous to place in position.
2.—That they cannot be tested when moored.
3.—That they are as dangerous to friend as to foe, when once placed in action.
4.—That an exploded, or known damaged mine cannot be replaced.
Note.—The above objections, especially 2 and 3, constitute without doubt very serious defects in a system of defence by mechanical mines, and in the case of purely mechanical ones, it seems almost impossible to eradicate any of them, though, notwithstanding, under the particular circumstance before-mentioned, these species of defensive torpedo will be found extremely useful.
The Advantages of Mechanical Mines.—They possess a few advantages, which are as follows:—
1.—They are comparatively cheap.
2.—They can be kept in store and ready for use at a moment's notice.