Why does Japan primarily use 3 foot 6 inch (narrow) gauge?

[frankmoh]

Was it something to do with the first trains in the country?

 

[hexagon789]

Was it something to do with the first trains in the country?

I believe so.

The British engineer, Edmund Morel, overseeing the first railway line to be constructed in Japan, had previous experience with building railways in New Zealand - which also uses 3ft 6in 'Cape Gauge'.

 

[Gag Halfrunt]

One explanation is that Edmund Morel, the civil engineer who built the first railway in Japan, had previously worked on Cape gauge lines in New Zealand.

Edmund Morel (engineer) - Wikipedia

en.wikipedia.org

 

[etr221]

For some historic background, the East Japan Railway Culture Foundation published a series of articles on Japanese Railway History in their English language magazine JRTR (Japan Railway & Transport Review), downloadable from https://www.ejrcf.or.jp/jrtr/history/index_history.html. There is also a feature on the Origin of 3'6" Gauge in Issue 31 of JRTR - see https://www.ejrcf.or.jp/jrtr/backissue/index_backissue.html for download link.

 

[Krokodil]

Presumably the terrain has a lot to say about why a narrow gauge was chosen for sub-Saharan Africa, New Zealand and Japan.

 

[Roast Veg]

It's also not too surprising that British export locomotives tended to be narrow gauge, owing to the shipping.

As for why Japan didn't widen the gauge after the late 1800s - the line was fully connected all the way from Tokyo to the Keihanshin area very quickly, and couldn't really be altered piecemeal.