Revision 2 In February 1944, the Imperial Naval General Staff (NGS) began developing a plan for a night strike on the American Fifth Fleet's anchorage at Majuro in the Marshall Islands. The plan, coded YU-GO Sakusen, called for the IJN’s First Mobile Force to depart the Inland Sea and attack Majuro with over 500 carrier-borne aircraft and some 300 land-based planes. Five submarines would launch 10 amphibious light tanks equipped with torpedoes that would attack the carriers in the anchorage. Two other submarines would land Special Naval Landing Force troops to attack shore installations. In March 1944, YU-GO was approved by Admiral Shimada Shigetaro (former CO of HIEI), Chief of the NGS and Admiral (Fleet Admiral, posthumously) Koga Mineichi (former CO of ISE), CINC, Combined Fleet, but at month’s-end Koga was killed when his flying boat crashed in bad weather enroute from Palau to Davao. YU-GO languished for lack of leadership while a new CINC, Combined Fleet was selected and appointed. Meanwhile, the First Air Fleet’s Cdr (later Captain) Fuchida Mitsuo, leader of the attack on Pearl Harbor, developed a small-scale plan for attacking Majuro. It was called Operation TAN. After a reconnaissance mission from Truk, Fuchida would lead a strike on the American carriers at Majuro with 27 torpedo-planes with LtCdr (Captain, posthumously) Egusa Takashige leading 27 dive-bombers.  Operation TAN was dependent on reconnaissance. LtCdr (Captain, posthumously) Chihaya Takehiko (62nd), of the 121st Naval Air Group's (NAG), directed two single engine Nakajima C6N1 Saiun "Myrt" long-range reconnaissance planes to take off from Tinian on 3 June 1944, refuel at Truk and then fly to Nauru to refuel again before the reconnaissance mission. The three-seat C6Ns had a cruising speed of 210 knots and a range of 1,663 nautical miles. Chihaya joined the two C6Ns on 4 June. That night he flew to Majuro, timing his flight to arrive at dawn 5 June, the hour of the initial proposed attack. He found eight fleet and four escort carriers in the anchorage. Chihaya took pictures and flew back to Truk. After refueling, he flew to Tinian to deliver the recon photos to Fuchida. Chihaya was to fly another recon mission immediately, but American air strikes on Truk prevented the mission. On 9 June 1944, LtCdr Chihaya flew a final reconnaissance flight from Truk to Majuro and back to Nauru and Truk, but found Majuro's anchorage empty. Vice Admiral (later Admiral) Raymond A. Spruance's Fifth fleet had departed to invade Saipan in the Marianas in Operation “Forager.” TAN No. 1 was cancelled. In September 1944, after the capture of the Marianas and Peleliu, Ulithi became the anchorage for the U.S. Pacific Fleet. An atoll made up of groups of islands in the Western Caroline Islands, 350 miles SW of Guam, Ulithi was the nexus of preparation for the assaults on Iwo Jima and Okinawa. The huge anchorage could hold over 1,000 large ships -a capacity greater than either Majuro or Pearl Harbor. Headquarters, Combined Fleet worked up a new plan for an attack on Ulithi. Cdr Nomura Ryosuke, a former SORYU fighter unit leader, drew up a scaled-down version of the previous plans. The new plan included the use of "kamikaze" suicide (tokko) planes that achieved spectacular (but overrated) success during the Battle of Leyte. Whereas the early plans relied on technical innovations, the new one stretched the limits of existing technology calling for an almost a ten-hour flight from Kyushu to Ulithi. Just as they had for YU-GO, the Japanese felt successful implementation of the new operation would result in a paralyzing blow for the Americans and become the "turning point of the war”. The main objective of Operation TAN No. 2 was to attack the American fleet as it lay anchored at Ulithi. The CINC, Fifth Air Fleet, Vice Admiral Ugaki Matome (former CO of HYUGA) approved TAN No. 2 with enthusiasm. Implementation of the plan, initially planned for late February, was delayed, but on 7 March 1945, the Azusa Tokubetsu Butai (Azusa Special Attack Unit) was established.  TAN No. 2 would use twenty-four Yokosuka P1Y Ginga (Milky Way) "Frances"twin-engine bombers, originally of the 762nd NAG. The three-man P1Ys had a cruising speed of 200 knots, a 1,036 nautical mile range and could carry two 500-kg bombs or a single 1,764-lb. torpedo. Five four-engine Type 2 Kawanishi H8K2 “Emily” flying-boat pathfinders of the 801st NAG and four land based bombers were to provide weather reconnaissance, advance patrols and lead the Special Attack Unit's Ginga bombers to Ulithi. The 10-man H8Ks had a cruising speed of 160 knots and a range of 3,888 nautical miles. In early February 1945, the 141st NAG based at Kisarazu on Tokyo Bay received an order to dispatch a detachment of seven C6N Saiuns to Truk. On 11 February, the C6Ns Saiuns took off. Two soon returned to base and one ditched en route. After an overnight stop at Chidori airfield, Iwo Jima, four C6Ns landed at Truk, but one was wrecked on landing. The C6N, designed for use by carriers, required specialized servicing, but there was neither fuel nor spare parts for the type available at Truk. The IJN's Sixth Fleet deployed three submarines to support the strike. The big 2,607-ton Type B-3 I-58 under Cdr Hashimoto Mochitsura (later, victor over INDIANAPOLIS) was to serve as a radio beacon for the P1Y Gingas. The small 370-ton cargo submarine HA-106 skippered by Lt Okakita Akimasa (former CO of RO-67) was to cruise off Minami Daito Jima to pick up ditched aircrews. On 5 March 1945, HA-106 was attached to the 5th Air Fleet and departed Kanoya on 8 March to patrol off Minami-Daito Jima, about 500 miles NNW of the location of the I-58. The 1,779-ton Type D1 transport submarine I-366, completed in October 1944, had made one supply run to Pagan Island. Now under the command of Lt (jg) Tokioka Takami (former CO of RO-67), I-366 was tasked to carry out a similar voyage to Meleyon Islet in the Woleai Atoll via Truk. Prior to her departure, a Type 13 air-search radar was installed in addition her Type 22 surface-search radar. Finally, on 29 January, all was ready and at 1300, the I-366, carrying 60-tons of cargo, including 33-tons of avgas, departed Yokosuka. ComSubRon 7 Rear Admiral Owada Noboru and most of his staff were present to see Lt (jg) Tokioka off, a mark of the importance attached to the I-366's mission. Tokioka's voyage was plagued by technical accidents from the start. To Admiral Owada’s chagrin, the I-366 soon signaled she was returning to base – her short-wave antenna had a serious defect. Repairs began immediately and eight hours later the submarine again departed, a Kikusui (Floating Chrysanthemum) pennant flying proudly from her conning tower.  The I-366 spent the night off Tateyama at the southern tip of the Boso Peninsula. At 0300 the next morning, Tokioka raised anchor and headed south. A few days later, the I-366 encountered a low-pressure area. The barometer dropped to 739-mm and the wind speed increased to 20 knots. While travelling on the surface, the I-366 struggled against 30-foot waves that flooded her diesels repeatedly and carried away a significant part of her deck cargo. By 10 February 1945, the weather had improved. At 0448, a lookout reported a cruiser on a southwesterly bearing . The transport I-366 had neither torpedo tubes nor any other means to attack the enemy. When two more vessels appeared on the horizon to the south, Lt (jg) Tokioka dove to 200 feet to continue his mission. Early in the morning, the I-366 surfaced off Moen Island at Truk and contacted the submarine base. Tokioka was advised not to enter the anchorage because of enemy air activity. The I-366 submerged and surfaced at 1230. Her cargo was unloaded but the operation took a long while. After nightfall, the I-366 departed the anchorage and headed for Meleyon. The ground crews at Truk made good use of the materials delivered by the I-366. Early in the morning of 13 February, the only flyable C6N Saiun took off for a reconnaissance sortie over Ulithi. Flying at 42,650 feet approaching the anchorage, the observer decided not to use the long focal length F-8 camera installed in the rear fuselage – there were no carriers at Ulithi. He did take a few pictures with his hand-held camera. IJN photo interpreters at Truk later found the entrance to Ulithi's anchorage was protected with anti-submarine nets, apparently installed after a kaiten attack in November 1944. After landing back at Truk, the pilot reported the results of the flight directly to Vice Admiral Hara Chuichi (former CO of TATSUTA), CINC, Fourth Fleet. Hara sent a coded report to Headquarters, Combined Fleet at Hiyoshi, in Kanagawa Prefecture. After receiving Hara's message, Admiral Toyoda Soemu, CINC, Combined Fleet, decided to postpone the operation until early March. On 5 March 1945, a C6N Saiun photographed 16 carriers at the Ulithi anchorage. On 9 March, a C6N piloted by Lt Miki Takuma (70th) with WO Ito Kunio (navigator) and CPO Hataya Shigeru (radio) discovered and photographed six fleet carriers and nine escort carriers of Task Force 58 at Ulithi. Ito also spotted a group including four carriers entering the atoll from the northeast. CPO Hataya then sent a message with the sighting details to Vice Admiral Hara and Admiral Toyoda. Enroute back to base, Lt Miki's C6N escaped from three P-38 "Lightnings" somewhere between Ulithi and Truk. After landing at Truk, IJN intelligence identified the carriers from Ito's photos as one SARATOGA type, four ESSEX types, three INDEPENDENCE types, seven escort carriers and four unidentified ships. When Admiral Toyoda received this information, he designated 11 March as D-Day.  That same day, submarine I-58, carrying four "kaiten" suicide submarines, was enroute to Iwo Jima to attack Vice Admiral Spruance's 450-ship invasion fleet, but LtCdr Hashimoto was recalled to Okino-Torishima (aka Douglas Reef) to participate in TAN No. 2. Hashimoto expected to arrive at the kaiten's launch position off Iwo in the next 1.5 hours. Disgusted at having to abort his mission when success appeared imminent, Hashimoto jettisoned two of his four kaiten and the I-58 proceeded at full speed towards Okino-Torishima traveling surfaced most of the time. Hashimoto was worried about the reefs in the area, but sunset on 10 March revealed that his navigator Lt Izuno Shozo had done a fine job. Okino-Torishima was visible dead ahead like a "lonely stone lantern” sticking out of the water. On 11 March 1945, Vice Admiral Ugaki addressed the Azusa Special Attack Unit before their take off. He noted that being chosen for the mission was a great honor. Ugaki stressed the seriousness of the hour, with "B-29s raiding our homeland every day" and Iwo Jima being doomed. There were supposed to be nineteen American vessels in Ulithi. The key to success laid in reaching the target area unsuspected. If the mission commander considered the chance of success small, they should not hesitate to return to base for another try later. The Combined Fleet also sent a message extolling this "divine chance. . . . Go forward, all of you, pledging yourself to defend our sacred land by surely destroying the arrogant enemy by ramming yourself into the enemy." The weather at Kanoya airfield on Kyushu was fine, but the departure of the 801st Ku's H8K Emily weather reconnaissance flying boat from Kagoshima was delayed. It finally got airborne just two hours before the Special Attack Unit took off. The Emilys were divided into two units. The first unit consisted of three flying boats, including the weather reconnaissance flying boat, and the second unit consisted of two planes. The H8K's were to guide the P1Y Gingas to Minami-Daito Jima and then return. One of the second lead unit's H8Ks took off at 0800. Take-off of the first lead unit was delayed about twenty minutes because of engine trouble. At 0900, twenty-four Yokosuka P1Y Ginga attack bombers led by Lt Kuromaru Naoto (67th) took off on a one-way "tokko" (suicide) mission to Ulithi. Each Ginga carried a single 1,764-lb bomb. At 0920, the Gingas set course due south from Cape Sata, twenty minutes later than scheduled. About four hours into the mission, the formation passed the submarine HA-106 off Minami-Daito Jima. Five P1Y s turned back because of engine troubles and later landed on Minami-Daito Jima. Three Gingas crashed. It is uncertain whether HA-106 rescued any of the aviators. She returned to Kanoya on the same day and then returned to her station in the Minami-Daito Jima area for two more days. The submarine I-58 took up station off Okino-Torishima and functioned as a radio beacon for the bombers. After Hashimoto’s Type 13 radar crew picked up the approaching planes, the submarine sent out a continuous long-wave radio signal. The P1Ys were flying at 6,560 ft and none of their pilots saw the island, but the H8K Emilys registered Hashimoto’s signals. The Emily weather reconnaissance plane turned back from near Okino-Torishima and returned to Kagoshima about 1530.
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