The Kaidai Type VI, also called the I-168 class, were built under the Maru 1 Programme and the Maru 2 Programme. They were faster than their predecessors, having the highest surface speed of any submarines in the world in the mid-1930s. However, their speed was surpassed slightly by later IJN submarines.
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The Kaidai VI contributed to sinking two USN aircraft carriers during World War II.