All and Nothing
After Pearl Harbor, the Japanese planned to strike the United States with aircraft borne by giant submarines. If it worked, the Atlantic fleet would be trapped.
- By Thomas S. Momiyama
- Air & Space magazine, November 2001
(Page 3 of 8)
Three empennage tips, folded for hangar stowage, were flipped up and locked into place. The floats, when used, were mechanically rolled out of separate stowage tubes on both sides of the hangar tube as the aircraft was emerging. They were snapped onto the pylons and then onto the underside of the wings with four quick-locking pins at each float’s eight attach points.
The foldaway design continued inside. A 13-mm machine gun mounted behind the navigator’s seat was stowed upside down in a recess in the fuselage and rolled rightside up into shooting position, facing aft to confront pursuers. For this manipulation, the aft end of the cockpit canopy was rolled upside down and away into the same stowage space below. In the up position the gun mount was hooked up to the gunner’s seat and aimed by the gunner, who used a pedal to adjust the seat vertically.
As this was to be a dive bomber, it had to be equipped with an aerodynamic dive brake to control the speed and angle of dive. Ozaki’s team employed a double-slot design that combined the flap with a dive brake, an idea Aichi had successfully developed for its carrier-based attack bomber, the B7A2 Ryusei (Allied code name “Grace”). The combination flaps extended fully to lower the landing speed to 78 mph. Only the smaller flaps deployed in the dive-brake mode at continuously selective angles down to the maximum 90 degrees. The pilot would select flap or dive brake mode and flip a switch at the top of the control stick while on approach or in dive bombing.
For the one-shot raid the Japanese navy would use the largest bomb in its inventory—the 1,764-pound general-purpose bomb with a steel penetrating head—or a 1,808-pound torpedo. The back seater’s primary duty was precision navigation to the target and back to the sub. This navigator-bombardier-gunner would sit in a swivel seat, usually facing forward. His panel was equipped with a set of navigation and communication gear well beyond those of most Japanese single-engine bombers.
Aboard the submarine, the aircraft was mounted at four attach points to a dolly that rolled on a rail to the inclined catapult, then served as the launching shuttle during the the catapult’s 69-foot power stroke until the aircraft separated from the dolly and flew away. The launching dolly was equipped with an articulated support structure so that the aircraft would be in a low-silhouette squat position while in the hangar tube and, when rolled out of the tube onto the catapult track, would be tilted nose up for higher angle of attack during launch. The aircraft was launched in the same manner even when the floats were attached to the aircraft. The floats straddled the catapult ramp without touching the sides of the ramp or the deck surface below.
As the aircraft design evolved early into adapting the detachable floats, a somewhat subtle but potentially significant consequence developed. Both the chief and assistant test pilots, Tadashi Funada and Yukitaka Murakami, were trained and experienced solely in floatplanes flying reconnaissance missions, not in bombers. So were the squadron commander, Lieutenant Atsushi Asamura, and the rest of the pilots assigned. The inexperience of the floatplane pilots in dive bombing and torpedo launching, along with the limited time available for developing the additional skills, reportedly led the unit to abandon the use of torpedos. Further, in training and in mission planning, only a shallow dive was employed in attacks to get the best accuracy attainable within the pilots’ limited expertise. This is ironic because the Seiran was one of the few aircraft in the world designed to be capable of both torpedo attack and dive bombing—besides being the first and perhaps the last sub-launched manned attack aircraft.
The Pacific war developed into the drawn-out match that Yamamoto had feared: It was a contest of national wills, armed might, and, more critically to Japan, industrial capacity. The main theater of war soon contracted to the southwestern rim of the Pacific and drew ever closer to Japan’s mainland. On a tour of Japanese naval bases undertaken in a desperate attempt to boost the morale of the troops holed up in the scattered last bastions of the crumbling Empire, Yamamoto’s airplane was shot down by an American P-38. With the death of the brilliant strategist, the Imperial Japanese Navy lost the force of his vision to “reach” the U.S. mainland. But the rapidly changing war situation may already have rendered the operation futile.
In 1944, war production in mainland Japan was in a shambles. The Japanese were fighting to defend what was left in Sokoku (ancestor’s land). Performance and expediency, certainly not engineering elegance, had become the operative words of the military and industry. Yet at the Aichi Aircraft Company, under the watchful eyes of the Kugisho, production of the M6A1 reached 28. Four I-400-class sen-toku were being built. The I-400 and I-401 entered service with their aircraft, and the I-402 was converted to a transport submarine. A fourth one was destroyed by a U.S. air raid on its shipyard.