(Imperial War Museum photo, scanned from "Submarines of the Imperial Japanese Navy" by Polmar and Carpenter)

I-55 running trials in Hiroshima Bay, 1927.

These were large double-hull boats derived from the previous KD1 and KD2 types, but with strengthened hull components.  This type is actually two slightly different classes, KD3A (I-53, I-54, I-55, and I-158) and KD3B (I-156, I-157, I-159, I-60, and I-63).  The latter were 16 inches (40 cm) longer than shown in the table below, due to a different bow shape.   I-63 was lost along with her crew in a collision with I-60 in 1939 .  Her hull was refloated and scrapped in 1940.  I-60 was lost January 17, 1942 to HMS Jupiter.  The remaining seven were employed in training duties for the remainder of the war (which explains their survival), and were either scrapped or scuttled shortly after the war.  Note: I-156, I-157, I-158, and I-159 were originally numbered I-56, I-57, I-58, and I-59 respectively, but were renumbered in 1942.