It's undisputed that the ship was, at least, carrying over 4 million rounds of ammunition (.303, suitable for use in British machine guns, and purchased from Remington), over 1271 cases of 3 inch shells (4 shells per case) and other items of war. More here: http://www.lusitania.net/index.html
roughly quoting Mark Twain. “The problem with some is not what they don’t know; its what they do know, that just ain’t so.”