I communicate herewith a letter from the Secretary of War, with accompanying papers, in response to a resolution of the Senate of the 21st ultimo, upon the subject of damages which will be "incurred by the United States in case of the repeal of so much of the act of March 3, 1855, as provides for the construction of an armory in the District of Columbia," and also a further answer from the Secretary of War to the resolution of the Senate of the 7th ultimo, requesting a full report of the steps pursued in execution of the clause of the act making appropriations for the civil and diplomatic expenses of the Government, approved March 2, 1855, which provides for the construction of the armory in this District before referred to. FRANKLIN PIERCE. WASHINGTON, _May 15, 1856_. _To the Senate and House of Representatives_: I transmit herewith reports of the Secretary of State, the Secretary of the Navy, and the Attorney-General, in reply to a resolution of the Senate of the 24th of March last, and also to a resolution of the House of Representatives of the 8th of May instant, both having reference to the routes of transit between the Atlantic and Pacific oceans through the Republics of New Granada and Nicaragua and to the condition of affairs in Central America. These documents relate to questions of the highest importance and interest to the people of the United States. The narrow isthmus which connects the continents of North and South America, by the facilities it affords for easy transit between the Atlantic and Pacific oceans, rendered the countries of Central America an object of special consideration to all maritime nations, which has been greatly augmented in modern times by the operation of changes in commercial relations, especially those produced by the general use of steam as a motive power by land and sea. To us, on account of its geographical position and of our political interest as an American State of primary magnitude, that isthmus is of peculiar importance, just as the Isthmus of Suez is, for corresponding reasons, to the maritime powers of Europe. But above all, the importance to the United States of securing free transit across the American isthmus has rendered it of paramount interest to us since the settlement of the Territories of Oregon and Washington and the accession of California to the Union. Impelled by these considerations, the United States took steps at an early day to assure suitable means of commercial transit by canal railway, or otherwise across this isthmus.