When launched on July 3rd, 1935, IJN I-7 and her sister-ship, IJN I-8 ,represented the largest submarines ever put to sea by the Empire of Japan to this point. As designed, these vessels were primarily intended for long-range reconnaissance work and thusly granted good sea-keeping qualities, strong armament and over-the-horizon capabilities through support of a single recoverable floatplane. Indeed, the boats were long endurance types with the ability to remain at sea for a consecutive period of 60 days and its operational ranges reached some 14,000 nautical miles - though highly dependent on food and fuel management. I-7 held a maximum speed of 23 knots and could dive to depths of 325, both proving useful in combat situations. Despite its reconnaissance-minded role, I-7 was well armed through 6 x 533mm torpedo tubes as well as a single 140mm deck gun for surface work. With its ability to launch a floatplane aircraft for scouting work, I-7 also featured a crane for self-recovery of said aircraft. This provided the boat with a good self-sustained operational existence which proved critical in ongoing Japanese naval operations in the vast Pacific Ocean region.
Power for the boat was served through a diesel-electric arrangement driving two shafts. The diesel powerplants provided the necessary propulsion when the vessel was surfaced while the electric motors gave the boat its lifeblood when submerged. When surfaced, the vessel could make normal headway at 16 knots and, when submerged, maximum speed fell to 8 knots.
Her overall profile was traditional for the period with a tapered bow and stern. The sail was managed at midships in the usual way and home to periscope, antenna and communications arrays. The twin screws were fitted at the stern to either side of the hull. A rudder at the extreme aft-end of the boat allowed for turning. Dive planes were featured at the bow as were the six torpedo tubes. The deck gun was fitted forward of the sail. Her entire crew complement numbered 100.
I-7's ocean-going career ended on June 22nd, 1943 when she was targeted and chased down by the U.S. Navy destroyer USS Monaghan (DD-354), the I-7 landing on a rock bed and given up by its crew near the Aleutian island chain. Her sister, IJN I-8, fared a little better but she too was sunk by American warships - this during the landings at Okinawa.