Naval infantry

Naval infantry is a capability, not necessarily a type of military unit, indicating that the personnel normally aboard a naval ship can engage in direct infantry combat with enemy personnel. Before the 20th century, the capability was common both for operations where the naval infantry force landed on a coast, but also when they would board another ship and engage the other crew with individual weapons. Even when ships carried personnel designated as "marines", it was common for "sailors" to participate in boarding or limited amphibious operations. For coastal raids, even if the sailors' role was to operate the boats that carried marines to the shore, the possibility of resistance at the point of landing meant that those sailors had to be able to defend themselves against individual attack.

Even in modern navies with a separately organized Marine force, there may well be additional infantry capabilities in naval personnel attached to the navy. To take the example of the country with the largest marine organization, the United States Marine Corps, there have long been infantry capabilities. In the Second World War, naval personnel that might well find themselves in hand-to-hand combat included:

• Construction battalions ("Seabees")
• Underwater demolition teams (UDT), "Frogmen"
• Amphibious boat crews
• Naval Beach Battalions (NBB), whose mission, today, is "NBG mission is to provide naval elements to the Amphibious Task Force to support the landing of a Marine Expeditionary Force (MEF) or to the Maritime Pre-positioning Forces to offload equipment and supplies for a Marine Air-Ground Task Force (MAGTF). A Beachmaster Unit was later commissioned for the purpose of maintaining the special teams to control boat traffic and conduct boat salvage operations in the surf."
• Beach jumpers

Also in WWII, while there were frequent mentions of "Japanese marines", Japan had no marine organization. It did have Special Naval Landing Forces. Some of the first Japanese actions in the SOuthwest Pacific, beginning on 11 Janyary 1942, Japanese naval landing troops, including paratroopers, occupied sedveral Australian-garrisoned islands in the Celebes. Army forces followed them up, and airfields on these islands were used to conduct air raids on Australia.