From the opinions given as to the number of gun-boats necessary for some of the principal seaports, and from a view of all the towns and ports from Orleans to Maine inclusive, entitled to protection, in proportion to their situation and circumstances, it is concluded, that to give them a due measure of protection in time of war, about two hundred gun-boats will be requisite. According to first ideas, the following would be their general distribution, liable to be varied on more mature examination, and as circumstances shall vary, that is to say:-- To the Mississippi and its neighboring waters, forty gun-boats. To Savannah and Charleston, and the harbors on each side, from St. Mary's to Currituck, twenty-five. To the Chesapeake and its waters, twenty. To Delaware bay and river, fifteen. To New York, the Sound, and waters as far as Cape Cod, fifty. To Boston and the harbors north of Cape Cod, fifty. The flotilla assigned to these several stations, might each be under the care of a particular commandant, and the vessels composing them would, in ordinary, be distributed among the harbors within the station in proportion to their importance. Of these boats a proper proportion would be of the larger size, such as those heretofore built, capable of navigating any seas, and of reinforcing occasionally the strength of even the most distant port when menaced with danger. The residue would be confined to their own or the neighboring harbors, would be smaller, less furnished for accommodation, and consequently less costly. Of the number supposed necessary, seventy-three are built or building, and the hundred and twenty-seven still to be provided, would cost from five to six hundred thousand dollars. Having regard to the convenience of the treasury, as well as to the resources of building, it has been thought that one half of these might be built in the present year, and the other year the next. With the legislature, however, it will rest to stop where we are, or at any further point, when they shall be of opinion that the number provided shall be sufficient for the object. At times when Europe as well as the United States shall be at peace, it would not be proposed that more than six or eight of these vessels should be kept afloat. When Europe is in war, treble that number might be necessary to be distributed among those particular harbors which foreign vessels of war are in the habit of frequenting, for the purpose of preserving order therein.