The vast majority of this collection is concerned with Johnston's work at Bethlehem Steel: correspondence, specifications, proposals, memos, blueprints, salary records, pamphlets, and photographs. A much smaller portion consists of strictly personal papers, such as family correspondence, and class notes from college.

The material has been grouped into three series: Correspondence, Reports and Tests, and Miscellany.

The correspondence files of Series I cover such subjects as ordnance contracts with Argentina, Brazil, Chile, Cuba, Italy, Russia and Turkey in the pre-World War I years (circa 1906-1913), general business correspondence and memoranda, sales letters, promotion notices, proposals and inquiries, etc. Correspondence regarding Bethlehem Steel's patent infringement suits with Midland Steel and Niles-Bement-Pond Company (1905-1909) are included. Also covered is the construction of an oil refinery in Argentina and the ore mines in Cuba, Puerto Rico, New York and New Jersey.

These topics generated large amounts of correspondence with a narrow focus. This Johnston filed by subject. In addition, Johnston corresponded with a large number of individuals and companies about a wide range of topics. These letters he filed by correspondent. Some correspondents rated their own individual file, while others, with whom Johnston corresponded infrequently, were grouped together in alphabetical folders. Series I reflects this system. Johnston filed his letters both by subject and by correspondent. Subseries A contains letters filed by correspondent, while Subseries B contains letters filed by subject.

Series II, Reports and Tests, contains twelve subseries: Armor Plate, Blast Furnaces, Financial, Processes & Equipment, Guns, Industrial Relations, Inspection Trips, Miscellaneous Reports, Notes & Notebooks, Plant Expansion, Rails, and Tool Steel.

Series III consists of contracts and notes concerning legal contracts and a single account book. The book is for a shipping company and covers the years 1867-1882. It appears to have no connection with Johnston, his family, or any other papers in the collection. The book was received with the rest of the collection, however, and so is filed with it.

There are two significant gaps in the Johnston papers. First, there is almost no material on Johnston's early career with Bethlehem dating from 1889 to 1892. All his printed biographies say that he was put in charge of the construction of the new armor plate and gun forging plants, yet there are no papers relating to those activities. This is especially unfortunate since Bethlehem had great trouble in producing its first armor plate, and the plant itself suffered many construction delays. Johnston's papers could provide valuable insight into the nature of these problems. This void is doubly intriguing when one considers that John Fritz's autobiography makes no mention of Johnston in its discussion of the construction of the armor and gun plants.

Second, there are no papers relating to foreign arms sales during World War I. This is unfortunate since Johnston was the chief foreign ordnance salesman, and since Bethlehem sold munitions to the Allies prior to America's entry into the war.