To the navy alone must we look for the defence of our shipping upon the high seas; but it cannot replace fortifications in the protection of our harbors, bays, rivers, arsenals, and commercial towns.
Let us take a case in point.

For the defence of New York city, it is deemed highly important that the East River should be closed to the approach of a hostile fleet at least fifteen or twenty miles from the city, so that an army landed there would have to cross the Westchester creek, the Bronx, Harlem river, and the defiles of Harlem heights--obstacles of great importance in a judicious defence.

Throg's Neck is the position selected for this purpose; cannon placed there not only command the channel, but, from the windings of the river, sweep it for a great distance above and below.

No other position, even _in_ the channel itself, possesses equal advantages.

Hence, if we had only naval means of defence, it would be best, were such a thing possible, to place the floating defences themselves on this point.