The Japanese coastal defence according to the Dutch magazine Marineblad dated 1926 no. 3

An item referred to the Revue Maritime dated March 1926 no. 75 reporting that Japan strengthened her coastal defence while it was impossible to strengthen the fleet lacking funds regarded a eventually war with the USA. The air force was to play a major role in this defence and at strategically points were 40,6 and 45,7cm guns to be placed and finally seemed Japanese shipyards to be building around 30 giant submarines armed with 20,3cm guns and carrying with them 2 bombers. These submarines seemed to have a very long range and able to be submerged during 10 days and that with a speed of 15 miles.