In addition to the provisions for the permanent forces on the Isthmus, additional field works will be provided to accommodate the 20,000 troops which might be brought to the Isthmus in case of war. These field works will take the form of barricaded positions, entrenchments, and other protective breastworks which will enable the troops to undergo a state of siege. It has been estimated by the engineers that behind such works as have been planned one defender can stand off six assailants, so that a body of 20,000 mobile troops under these conditions could hold the Isthmus against a siege of 100,000 for a reasonable time. These field works will be constructed principally around Gatun and Pedro Miguel. The buildings for the permanent force stationed on the Isthmus will be constructed on the unit system so that any necessary expansion can be made. The question of fortifying the canal was one which engaged the serious attention of Congress for a long time. There were two main viewpoints as to what policy should be pursued. One contention was that the canal should be made neutral, open to the ships of all nations, including the United States, on equal terms even in case of war between the United States and any other country. It was contended by those who took this view that to declare it neutral would render it immune from any attack and guarantee its perpetuity as a great commercial undertaking under the control of the United States. They contended, furthermore, that the United States was bound, under the terms of its treaty with Great Britain, to make the canal neutral and that to fortify it would be to violate the Hay-Pauncefote treaty. They asserted that the United States was under solemn obligations to recognize the principle of neutrality as applied at Suez and offered the express terms of the Hay-Pauncefote treaty in proof of their contention. This treaty provided that "the United States adopts, as the basis of the neutralization of such a ship canal, the following rules substantially embodied in the Convention of Constantinople, signed the twenty-eighth of October, 1888, for the free navigation of the Suez Canal; that is to say: "First, the canal shall be free and open to the vessels of commerce and of war, all nations observing these rules on terms of entire equality so that there shall be no discrimination against any such nation, or its citizens or subjects, in respect of the conditions or charges of traffic, or otherwise. Such conditions and charges of traffic shall be just and equitable. "Second, the canal shall never be blockaded, nor shall any right of war be exercised, nor any act of hostility be committed within it. The United States, however, shall be at liberty to maintain such military police along the canal as may be necessary to protect it against lawlessness and disorder.