Marines operate as expeditionary units and are completely amphibious. There were simulations of air combat, ballistic missile defense and amphibious landings. An airport for use by seaplanes and amphibious aircraft is called a seaplane base. Its heft restricts transport by C-130 cargo aircraft or amphibious ships. Naval aviation is also used as part of amphibious warfare. This Battalion specializes in Amphibious Warfare. The battle plan called for a combination of naval bombardments and an amphibious landing. The Observer Group was the first unit trained in amphibious reconnaissance. It can also include conducting amphibious reconnaissance. From 1924, it was used with landing boats in annual exercises in amphibious landings. The ROK Navy (ROKN) is responsible for naval and amphibious operations. The division began intensive training in amphibious landing operations. Marine forces evolved to specialize in the skills and capabilities required for amphibious warfare. The assessment was that the area was well suited for landing U.S. amphibious forces. The Navy deployed them on the decks of ships and for use in amphibious warfare.