Japanese 20mm Cannon Blockhouse, World War II defensive structure at Big Agingan Beach, Saipan, United States.
This blockhouse is a concrete military structure at Big Agingan Beach built to hold 20mm cannons behind thick walls with several firing ports. The building has a circular design with a steel entrance door and was part of the coastal defense network along the island's shore.
Japanese military forces built this defensive position in 1944 as part of their coastal defense system around the island. Allied forces captured it during the early stages of the Battle of Saipan as they advanced inland.
The National Register of Historic Places recognized this military structure in 1995 as a significant representation of Pacific War defense installations.
The site sits near the beach and is easy to walk to from nearby roads, with open access to the area around the structure. Visitors can study the exterior design and firing ports up close, though the ground is uneven and some parts of the building should be approached with care.
The blockhaus retains original steel sliding shutters at each firing port that allowed quick opening and closing during combat. These working details show how Japanese engineers designed practical solutions for rapid-fire operations at the defensive line.
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