"300X" was the name given to the Class 955 (955形) 6-car experimental Shinkansen train developed in 1994 by the Central Japan Railway Company (JR Central) in Japan to test technology to be incorporated in future shinkansen trains operating at speeds of 300 km/h (186 mph) or higher.

Manufacture of the train was shared among four different manufacturers, with a number of different body construction methods used. The two ends cars employed differing nose designs, and a number of pantograph shroud designs were tested over the lifetime of the trainset.

Cars 2 and 5 were fitted with pantographs.

End car with "cusp" nose design, built by Mitsubishi Heavy Industries. The body was constructed of rivetted Duralumin. This car had no passenger seats.

The body was constructed by Nippon Sharyo using large hollow aluminium extrusions. This was the only car in the trainset to be fitted with passenger seats.

This vehicle was constructed by Kawasaki Heavy Industries using spot-welded large aluminium extrusions and was fitted with active tilting.

This vehicle was constructed by Nippon Sharyo using large hollow aluminium extrusions, similar to car 2, and was equipped with large side doors for installing and removing test equipment.

This vehicle was constructed by Hitachi using aluminium honeycomb panels. This car had no seats.