The EOC 4-inch 50 caliber was a British naval gun designed by the Elswick Ordnance Company for export customers in the years before World War I that armed warships of the Republic of China and the Greek Navy. These ships served in both World War I and later World War II.
The EOC 4-inch 50 caliber began life as a design produced by the parent company of Elswick, Armstrong Whitworth for export customers called the Pattern P. These guns did not serve aboard ships of the Royal Navy.
The EOC 4-inch 50 caliber was constructed of an A tube and wire wound with a protective outer jacket. It also had a horizontal sliding-wedge breech and fired fixed quick fire ammunition.
EOC 4-inch 50 caliber guns armed coastal defense ships, destroyers and protected cruisers.