For a number of years many believed that Japanese mini-submarines successfully attacked the Pacific Fleet based at Pearl Harbor on December 7th 1941. However, there was never any hard-core evidence to support this belief - that Japanese mini-subs supported the aerial attack on 'Battleship Row'. Now, however, it is believed that sufficient evidence exists to support this view despite the massive anti-submarine defences that surrounded the naval base at Pearl Harbor.
Researchers such as Burl Burlingame now believe that the following happened:
- Five mini-submarines carried piggyback-style by normal submarines approached Pearl Harbor to within a couple of miles of the harbour entrance.
- All five mini-subs were released to approach their targets.
- Mini-sub Number 1 was sunk by 'USS Ward' and did not fire either of its two torpedoes.
- Mini-sub Number 2 got into Pearl Harbor and fired its two torpedoes. Both missed their targets, but Number 2 then sunk by two American warships.
- Mini-sub Number 3 ran aground and did not fire either of its two torpedoes.
- Mini-sub Number 4 was found in 1960 with both its torpedoes still on board. It now stands outside of the Japanese Naval Academy.
- However, no one knew what happened to mini-sub Number 5.
However, a submariner explorer based in Hawaii, Terry Kirby, believes that he has now solved the mystery. He claims to have found the remains of Number 5 three miles from Pearl Harbor. Lying on the sea floor, the remains of the mini-submarine are in three parts.
The mini-submarines built by the Japanese at the start of World War Two were highly secret. Similar ones built in Europe at the time were not as sophisticated as the Japanese ones - hence the desire for secrecy. Unlike European ones, Japanese mini-submarines were scaled-down versions of their normal submarines. Each of the seven compartments in the mini-subs was crammed with equipment. They were six feet wide and eighty feet long. Powered by a 600 hp engine they could travel at 19 knots - twice the speed of the submarines that piggybacked them to Pearl Harbor. Each mini-sub carried two 1000 lb torpedoes. Far more important for the research of Terry Kirby, was the net cutter found at the front of each craft. Numbers 1 to 5 had a net cutter shaped in a figure of 8 - unique to these five mini-subs. The mini-sub found three miles off of Pearl Harbor had this figure of 8 net cutter and confirmed that Kirby had indeed found Number 5.
The wreck also had a rudder only found on these five mini-subs. These rudders proved to be far too small and made each craft far from manoeuvrable. Later versions had bigger and more useful rudders.
Kirby also found that its two torpedoes were missing from Number 5 and presumably had been fired.
However, finding the wreck of Number 5 led to far more questions being asked.
The most obvious was whether Number 5 had successfully attacked any US ship in Pearl Harbor. For a number of years, some believed that the 'USS Arizona' had been hit by a torpedo fired by a submarine - along with others fired from Japanese aircraft.
Some believe however that Number 5 actually hit 'USS West Virginia'. The clue to this is a photo taken from a Japanese aircraft during the attack that may actually show Number 5 along with a torpedo trail heading towards 'USS West Virginia'. The photo is far from clear. Those who believe this theory claim that the three 'rooster tails' in the photo are proof of this. When a mini-submarine fired its torpedoes it experienced a significant loss of weight in the bow. This caused instability in the mini-sub that made it bob from bow to stern. This lifted the propeller out of the water for a short time causing a 'rooster tail'. This instability might also have been caused by a successful hit. The torpedoes fired by Japanese mini-subs weighed 1000 lbs - twice as much as the torpedoes carried by bombers. The shock waves caused by 1000 lb torpedoes hitting its target would have been sufficient to cause Number 5 to temporarily lift out of the water - creating 'rooster tails'.
Number 5 fired both torpedoes. If one hit 'USS West Virginia' what happened to the other? Survivors on the 'USS Arizona' claimed that they saw a torpedo trail heading towards their ship. With twice the explosive capacity of a torpedo carried by an aircraft, a successful impact would have been obvious. So what happened? The clue to this may be found in a Congressional report by Admiral Nimitz on the attack on Pearl Harbor that stated that an unexploded 1000 lb torpedo had been recovered - Japanese torpedo bombers carried 500 lb torpedoes. Therefore, though survivors may have seen a familiar torpedo trail, it seems as if the torpedo itself did not explode.
At 22.40 on December 7th, the submarine that had piggybacked Number 5 to Pearl Harbor received a Morse code message from it. The actual message translated as 'Kira'. However, the Japanese code for a successful attack was 'Tora', which translated as 'we have succeeded in our attack'. However, the Morse code difference between 'Kira' and 'Tora' was minimal and some believe that the radio operator on Number 5 simply made a mistake.
What happened to Number 5 after the attack? Clearly there can only be speculation regarding this. However, the accepted theory is that Number 5 sailed to a remote part of Pearl Harbor called West Loch. Here they scuttled the mini-sub. They had been ordered not to allow the craft to fall into the hands of the Americans and each of the five mini-subs was fitted with explosives charges just behind the conning tower.
However, if the crew of Number 5 did scuttle the mini-sub in West Loch, why has its wreck been found three miles off the coast of Pearl Harbor? The answer to this can be found in what was a closely guarded secret.
On May 21st 1944 Pearl Harbor experienced a second disaster. In preparation for the invasion of Saipan, American naval craft were gathering at Pearl Harbor. On this day, a landing craft in West Loch exploded and the explosion succeeded in destroying six other landing craft. Over 200 men were killed. Such a disaster could not be made public and the authorities ordered that West Loch should be cleaned up as soon as was possible with no obvious evidence of such a disaster. A major sweep of West Loch was made and anything on the seabed was 'collected' and dumped about three miles out at sea. It is believed that during this sweep the remains of Number 5 was swept up along with many landing craft and dumped. Hence why it is surrounded by many landing craft where it lies three miles out to sea.