Outfitted for extended patrols in the Indian Ocean, the AMCs also carried additional fuel, torpedoes and supplies for Japanese submarines thereby bestowing on them a secondary role as improvised submarine tenders. As envisioned in Tokyo, the raiders would emulate their Nazi partners by marauding as teams with Japanese submarines. In this manner a stream of fresh supplies could replenish the submarines without necessitating their return to base.
However, unlike their German counterparts, Japan's AMC marauders felt no compulsion to adopt the kind of clever deceptions employed so successfully by the German raiders. Disguises asseemingly innocent neutral merchantmen allowed the Germans to often draw very close to their prey before unfurling their true colors. It was often the shock value of looking down an enemy gun barrel at close range that minimized casualties by quickly convincing the enemy resistance was futile; that they could neither out-run, out-gun nor out-fight their adversary.
GIDDY WITH VICTORY, THE JAPANESE ADVANCE INTO THE INDIAN OCEAN
Following the lightning successes of their attacks on Pearl Harbor, Singapore, Hong Kong, the Philippines and Java, the Japanese Fleet - flushed with "Victory Fever" - flexed its muscle with a series of fast carrier strikes against British positions ringing the Indian Ocean. Calculated to stun what was left of the battered Royal Navy into virtual submission, late in March 1942 the Japanese invaded tiny Christmas Island in the Indian Ocean with the idea of building an airstrip there. Quickly overwhelming the 100-man British garrison, the Japanese soon hadsecond thoughts about building what could only be a small airfield on an isolated outpost. Abandoning the idea and the island, Nagumo's carriers next struck Columbo, Ceylon, on 5 April where they covered the landing of Adm. Oawa's large Second Expeditionary Fleet which struck and bombarded coastal positions south of Calcutta, east of India. Off Calcutta they also engaged in a cat and mouse game that left two British cruisers, two destroyers, a sub tender and supply ship sunk in its wake.
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The 10,439-ton Hokoku Maru was also built by Tama in 1939. Seen in 1942 the raider wears camouflage paint designed by the Kure Navy Yard where she converted into a raider in 1941 with the addition of eight 5-in guns, two 21-in torpedo tubes, 25mm AA guns and two scout planes. Hokoku Maru was sunk 11 November 1942, by a Royal Indian Navy minesweeper.
Four days later Ozawa and Nagumo's ships and planes raided Tricomalee, Ceylon, in a three-pronged assault which netted 23 Allied freighters sunk for a loss of 116,830 tons at a cost of only a few Japanese aircraft. In four months of continuous action, not one Japanese ship had been lost. Even more telling, in Nagumo's final 150-plane raid on 9 April, the British light carrier HMS Hermes had been sunk 65 miles south of Trincomalee along with the Australian destroyer Vampire.
Having been at sea continually since 26 November 1941, Nagumo's carriers were sorely in need of refits; his weary flight crews long overdue for R&R. Leaving behind a small force of destroyers and light cruisers to guard their latest conquests, the seemingly invincible main fleet returned to Japan. Indeed, by May 1942, the IJN had run the Brits out of the Indian Ocean; had the Americans reeling in the Pacific, and stood at the gates of Australia, ready to invade Port Moresby.
Realizing that the Indian Ocean was pregnant with largely defenseless Allied shipping the Japanese moved the 8th Submarine Flotilla into the area. In addition to the flotilla's eight fleet-type submarines, three midget subs were carried piggy-back on the mother submersible's deck. Two of the 2800-ton "I-boats" also had Aichi floatplanes stored in tubular deck hangars.
Supporting the submarines were two of the large new Japanese merchant cruisers (AMCs) -Aikoku Maru and Hokoku Maru. Equipped with eight 5-in guns each, four 25mm AA guns, two 21-in torpedo tubes and two seaplanes, the raiders took up central positions along well-traveled trade routes which made them readily available to resupply the submarines, or attack the enemy at will.
The raiders did not have long to wait.
On 9 May 1942, the two marauders overtook and captured the 12-knot 7986-ton Dutch motor tanker SS Genota some 465 miles southeast of Diego-Suarez, Madagascar. An unarmed easy conquest, a prize crew was placed aboard Genota and she was soon commissioned in the IJN as the oiler Ose. A few weeks later a seaplane from the submarine I-10, flagship of the 8th Flotilla, overflew Diego-Suarez where she spotted the British battleship HMS Ramillies under repair. The following day I-16 and I-20 each launched their midget submarines. Breathless hours later, the harbor boomed with the sound of an exploding torpedo which luckily flooded only one of Ramillies compartments. Minutes later a second torpedo from the other mini- sub struck the tanker British Loyalty, sinking her on the spot. With clouds of thick black smoke darkening the sky British subchasers sprang into action rapidly depth-charging several sectors of the harbor.
In the melee one of the two-man midget subs ran aground on a shoal; its crew taken prisoner and later executed. The other midget was never seen nor heard from again; ostensibly sunk by depth charges.
Although this action marked the greatest success of the midget submarines, their mother subs and the two AMCs continued to ply the heavily traveled waters of the Indian Ocean adding considerable tonnage to their scores. Early in June Aikoku Maru and Hokoku Maru, steaming together, managed to sink the 6740-ton British freighter Elysia with shellfire. In nearby Mozambique Channel, the I-boats sank three cargo ships at the same time. Other submarine successes followed in rapid order which sent the bulk cargo ship Loch Loman and freighter Elknaren, among others, to the bottom. By 9 July, the I-boats had accounted for 18 vessels, or 146,680 tons of shipping lost to the Allies.
Not to be outshone by the submarines they supported, the two raiders managed to conclude their first successful patrol by catching and sinking their third victim; the 7205-ton Huakari bound from Fremantle to Columbo, Ceylon on 12 July. Caught sailing alone nearly 800 miles southeast of Diego-Suarez, the hapless Huakari succumbed to the pair's torpedoes. Sharing considerable jubilation over their victories the surface raiders and their undersea companions departed for a long anticipated period of relaxation if not rest with the bawdy ladies of Penang's infamous brothels.
IMPRESSIVE BOX SCORE FAILED TO IMPRESS THE HIGH COMMAND
A glance at the operational box score should have been persuasive evidence of the value of the AMC/submarine commerce raiding program. The Japanese had damaged a British battleship sufficiently to keep her out of the war for many months; had sunk 19 British merchantmen totaling more than 150,000 tons; caused the Brits to divert critically needed warships from other areas to search for the elusive raiders - all at a cost of only two midget subs and four men! Yet, oddly the Japanese mindset was blind-sided by the lure of still bigger naval game. Impatient for more notable success, the Japanese High Command elected not to continue the AMC/submarine raider program. Instead, the surface raiders would operate alone; the submarines deployed against the Allied Fleet.
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HMIS Bengal was one of four steel-hulled 650-ton Bathurst-class minewseepers built in Australia for the Royal Indian Navy. Similar to the Brit's Bangor-class, 38 Bathurst-class were built in Australia for the Royal Navy, but most flew Aussie flags. 186-ft long, they all served as 15-knot escorts; had a crew of 60 men and were generally referred to in the land down under as "corvettes."
By early fall of 1942, Japan's bloated sense of naval invincibility had been thoroughly shattered. The Battle of the Coral Sea nullified their plan to invade Australia and their costly defeat at Midway dulled the cutting edge of their offensive capability - their vaunted lost carriers and experienced air crews. Worst yet, Japan was now denied the leadership and insights of Adm. Yamamoto, whose plane had been ambushed and shot down over Bouganville by 16 American P-38s. Though Yamamoto's battle skills were questioned by many, he alone seemed to realize that Japan was fighting a war of logistics; that the ticking clock was its worst threat - the most critical element in their hope for ultimate victory. If Japan could not quickly consolidate its many conquests and continue to keep the Brits and Americans at bay, Yamamoto predicted Japan would lose the war!
Never having been in a commerce war Japan's hide-bound naval planners completely failed to appreciate the importance of interdiction - attacking enemy supply lines. Paradoxically, within months of removing their subs from the commerce/interdiction role their own merchant fleet began to be decimated by far-ranging American fleet submarines. In the end, it was the submarine - not the surface ship nor the carrier - that broke the back of Japan's vitally needed merchant fleet.
Defining the submarine's principal value as a fleet asset, Japanese planners insisted that I-boats hunt American warships even though attacking well-protected Task Forces was far riskier and less productive than going after plodding merchant men. Adopting these dangerous tactics Japanese losses soon mounted, prompting Tokyo to blame the submarine skippers not the manner in which they were foolishly deployed. As the complexion of the war changed and America gained control of the skies over the Pacific Japan's once formidable submarine force was further squandered by being relegated to carry troops and supplies to outposts which could no longer be logistically supported by surface ships. Diverted from the role for which they were designed, through no fault of their own Japan's submarine force soon ceased to function on a scale commensurate with their destructive potential.