As No.2 Sea Fort is located at the mouth of Tokyo Bay and has been exposed to the tidal current, wind and sea wave. So its circumferential revetment part has largely been collapsed. In addition, it was confirmed that sea water coming from this collapsed or damaged revetment has flooded artillery battery basement and sands of this island basement had outflowed to the sea. It is confirmed that deterioration, damages and collapse everywhere in No.2 Sea Fort.