The Harvard Mark I, or IBM Automatic Sequence Controlled Calculator, was one of the earliest general-purpose electromechanical computers used in the war effort during the last part of World War II.

The Mark I trench knife is an American trench knife designed by officers of the American Expeditionary Force for use in World War I.

a British tank of the Inter-war period built by Vickers from 1924.

The Mark 1, and later the Mark 1A, Fire Control Computer was a component of the Mark 37 Gun Fire Control System deployed by the United States Navy during World War II and up to 1991 and possibly later.

a British vehicle of the First World War.

In the United States military, the Mark I NAAK, or MARK I Kit, ("Nerve Agent Antidote Kit") is a dual-chamber autoinjector: Two anti-nerve agent drugs—atropine sulfate and pralidoxime chloride—each in injectable form, constitute the kit.