How big were the Japanese submarines?

Some were smaller than American boats and many were the same size or larger. Japan built a variety of submarines of different sizes and capabilities. It appears that there were as many as 11 different classes in service at the outbreak of the war and that Japan built an additional 15 new classes during the war.

Some examples were:

1. The older RO boats displaced from 700 to 1,000 tons. These were one-half to two-thirds the displacement of the U. S. 1,500-ton Gato/Balao/Tench class submarines.
2. The early “fleet boats” (the I-53 and I-68 classes) were shorter range boats that displaced about 1,400 to 2,000 tons. They usually would carry one scouting aircraft.
3. The I-13 class that displaced about 3,600 tons and carried two aircraft.
4. The I-200 class boats that displaced only about 1,000 tons but were capable of higher submerged speeds.
5. The I-400 class boats that displaced 5,200 tons. These boats had a range of as much as 37,000 nautical miles and carried three aircraft. These were the largest submarines anyone built until we commissioned the USS Benjamin Franklin class of nuclear powered, Polaris submarines in 1965. Yes, these WW2 Japanese submarines were actually larger than our earliest Polaris submarines.

NOTE: The US built only three new classes of submarines during the war that were very similar to each other. This strategy of fewer classes made it easier and more economical to design and build the boats, purchase components, train the crews, complete repairs and stock spare parts. However, they were general usage boats and may not have had features that some special operations required.