Alexander Mackenzie (May 25, 1844 – February 23, 1921) was an American engineer. Mackenzie was born May 25, 1844, in Potosi, Wisconsin and graduated from the United States Military Academy in 1864. Commissioned in the United States Army Corps of Engineers, he served with the Union Army in Arkansas in 1864-65. Mackenzie spent six years commanding a company of engineer troops at Willets Point, New York, that experimented in the use of torpedoes (a.k.a. mines) in coastal defense. In 1879 he began a 16-year stint as Rock Island District Engineer. He built 100 miles of wing dams on the upper Mississippi River and produced a 40-foot channel between St. Paul and the mouth of the Missouri River. Called to Washington in 1895, he became Assistant to the Chief of Engineers in charge of all matters re