Portal:Military history of Australia/Selected anniversaries/August/August 4
- 1914 – World War I: Great Britain declared war on Germany; as a result, Australia was also at war.
- 1914 – World War I: Fort Nepean, Victoria fired the opening shots of World War I, opening fire on the German merchant ship Pfalz.
- 1942 – World War II: Japan launches the first air raid on Milne Bay.