In addition to the hydro-electric plant, the Sanitary District constructed a lock to connect the Ship and Sanitary Canal to the I. and M. Canal, making the former navigable. At the controlling works four miles north, the Sanitary District engineer, Isham Randolf, designed a unique structure never built again– butterfly dam designed to control the Sanitary Canal flow by means of 18 valves or gates individually controllable and operated electrically.
The controlling devices were mostly removed or made inoperable when by law the Sanitary District was restricted in what it could divert from Lake Michigan, and so erected a guard lock at the mouth of the Chicago River, and used other methods for drawing water from the lake.
Besides the use of Chicago’s hydraulic infrastructure for the purposes of trade and commerce, water and sewage disposal, the last aspect of this hydraulic system was for national defense– a concern that is frequently motivated by irrational fears, yet it does move the people of this nation in strange but forceful ways. Since Lake Michigan was the only one of the Great Lakes entirely within the borders of the United States, and since this country and Great Britain had agreed not to put armed vessels on the Great Lakes, there was a fear that in case of war, Great Britain could send armed vessels from canals like the Rideau to gain control of what was called the Northern Frontier. In 1839 Captain Cram pointed out that one of the needs of a good harbor at Chicago was for defense. He wrote:
“The importance of Lake Michigan in a military point of view should not be overlooked. Its position with respect to the facilities of procuring provisions and for transportation, and its unequaled adoption for harbors into which armed steamers, and other armed vessels might retire for repairs and supplies, would add peculiar value to the inland sea. And in the event of war between the United States and the power in possession of all the lakes, Lake Michigan might become the scene of contention. A loss of its possession would be attended with consequences of serious import to the commerce, agriculture, and safety, of a large part of the West." 29
Cram’s argument was that this need necessitated Federal money for the Chicago port, as it was the best place to construct such a harbor.
By the 1860s, the concept of defensive needs had shifted to a canal which would provide a defensive link to the Mississippi and the Gulf of Mexico. This argument was put forward during the Civil War and after. In the summer of 1863, a National Ship Canal convention was held in Chicago to try and persuade the Federal government to construct larger canals into Lake Erie and from Lake Michigan at Chicago to the Mississippi. Naturally, part of the argument for such an effort was the commercial advantages in moving farm products east and south. However, the defense needs were heavily stressed. The memorial at the conclusion of the convention was sent to the President and to Congress. It states:
“We must, if practical, do as Great Britain has done–construct military canals adequate in capacity to admit our gunboats to the Lakes. Thus, we shall be placed upon an equality with our neighbors....
“Prominent among others, is that of enlarging the present Illinois and Michigan Canal from Lake Michigan to Joliet, a distance of 36 miles, and the improvement of the Illinois and Des Plaines Rivers, so that steamers and gunboats which navigate the Mississippi can pass directly into Lake Michigan at Chicago.
“The military position is, in a few words, this: On the American side, the Northern Frontier is defenseless. It is amply defended on the British side. England can take her gun-boats from the ocean through the canals and the