The 10-300 series ("ten thousand and three hundred" series) was developed for Toei Shinjuku Line and through-services to Keio lines. There are three groups, and there are many differences as if they are not the same type. In this article, they are classified into 10-300 series (E231-based), 10-300R series and 10-300 series (E233-based).
This group is based on JR East E231 series (commuter type), and share the same traction, similar bodies and bogies. Tokyo Metropolitan Bureau of Transportation decided that the series should be based on JR East's rolling stock to reduce costs. 12 eight-carriage units were delivered, and intermediate carriages were added to four units by 2010, which are now formed of ten coaches.
However, the rest of them (which are formed of eight coaches) were replaced with the 10-300 series (E233-based) in 2021-22 as a part of capacity-boosting programme for Toei Shinjuku Line. The Bureau might have found that refurbishing the E231-based 10-300 series would be more costly than introducing brand new trains.
The 10-300R series was formed of ten coaches, but each unit consisted of two 10-300 series (E231-based) carriages and eight 10-000 series carriages. According to the Bureau, R stood for "Repair" and "Reconstruction". In the early-2000s, the Bureau was planning to replace 10-000 series, but some intermediate carriages were less than 20 years old. Hence, the Bureau decided to reuse those younger coaches. That is why, front and intermediate carriages of the 10-300R series looked very different to each other.
There were six eight-car units, but withdrawal commenced in 2015 and completed in less than two years. They retired while a few 10-000 series still remained in service. The front carriages of the 10-300R series were scrapped just 10-12 years after introduction, being the shortest lifespan among all underground trains of the Bureau.
Front and intermediate carriages of the 10-300R series.
Since 2013, the Bureau has been introducing ten-car units of the 10-300 series, which this time are based on JR East E233 series (variant 2000). Thus, the new group is so different from the E231-based units that it is hard to believe that they are registered as the same type.
Trains of this group replaced the 10-000 series, 10-300R series and some 10-300 series (E231-based).
Current Operations & Future Prospects
The 10-300 series are used for Toei Shinjuku Line and through-services to Keio lines. All units are now formed of ten coaches.
