Secondary sources can be classified into at least two categories. One is scholarly materials, developed usually by professionally- trained historians, i.e., persons who have earned at least one graduate degree in history. Many such historians hold the Ph.D. and teach in a college or university. Such persons have skill and experience in making judgments about sources and in using critical thinking to interpret the facts they find in their research. Some amateur historians (i.e., historians without such credentials) have sufficient experience and/or judgment to write excellent scholarly history as well.
The other category of secondary sources is popular history. It is usually produced by non-professional historians, such as journalists, novelists, or other writers. Much of the secondary source material one finds on the Internet falls into this category. Usually, someone who is an enthusiast about a given historical subject (the American Civil War, some phase of it, etc.) decides to write about that subject, then puts that writing on the Internet. Such work is not subject to the criticism of historians, as is the case with much of the secondary source material written by professionally-trained historians and published as books or articles in historical journals. (For suggestions about evaluating secondary sources on the Internet, see the next section of this project, Evaluating History Resources Found on the Internet.)
There are relatively few recently-published secondary historical works on the Internet for at least two related reasons. One is that almost all such writing is copyrighted. Such works are for sale. In many cases, authors earn royalties on the profits made by publishers. Neither authors nor publishers wish to give away on the Internet that for which they would otherwise be paid. Also, professional historians who teach in universities publish materials in book or article form partly to obtain tenure or to seek promotion from one tenured faculty rank to another. In general, those persons who make decisions about tenure and promotion do not, at the present time at least, recognize historical writings produced directly for the Internet.
If you find (by searching with subject directories or search engines) any secondary sources which seem useful for your research assignment, I suggest that you note for each one the exact title, author, any information about the author of the source or the producer(s) of the site, and the Internet adddress (URL) of the document. Perhaps print out the documents (at least those that are brief). Then take all of this information to your course instructor to see if the materials will be acceptable.
(See Finding History Resources on the Internet with Subject Directories and Finding History Resources on the Internet with Search Engines for examples of some of the possibilities and problems of using both subject directories and search engines to find secondary sources for particular subjects.)
For the history of the United States Army, there is an important Web site, U.S. Army Center of Military History. The center is, according to its own information, "responsible for the appropriate use of history throughout the U.S. Army." It records "the official history of the Army both in peace and war." The term "official" is important, as it indicates that material produced by the center may not always be objective. Still, it appears that there are valuable secondary source materials here, although not many yet. There are materials on World War II, The Korean War, and the Gulf War. One such is The Women's Army Corps: A Commemoration of World War II Service, a book by Judith Bellafaire. Eventually, there are to be primary source government documents available at this site.