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wdolson -> RE: Destroyers without depth charge racks (10/14/2013 12:19:51 AM)
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IJN sub doctrine was very flawed from the outset. First off sub squadron commanders usually had little or no submarine experience. Then the primary doctrine was to use the subs as a scouting and thinning force ahead of the big battle. Both the US and IJN had standing orders that warships were their primary target, but US sub captains were encouraged to sink merchant shipping whenever they came across them and had freedom of action in achieving that goal. Whereas IJN sub captains had very strict rules about how many torpedoes could be fired at a given target type and were encouraged to pass up merchant targets in favor of warships.
As the war went on US subs were increasingly sent to patrol zones that were very rich in merchant targets, whereas IJN offensive sub operations were more often sent where they believed warships were. Warships are faster than merchant ships and once surprise is lost, the warships run up to full steam and clear out of the area very quickly. Merchant ships were often slower than surfaced subs and sometimes were slower than submerged subs, so a sub had more opportunity to maneuver into a better firing position on a merchant target. Most submarine sinkings of larger warships were serendipity of being positioned in the right spot at the right time, whereas a lot more merchant ships were sunk because the subs had more opportunities to get the right shot. (There were also more merchant ships out there too.)
Japan never changed their doctrine and redirected their subs towards merchant targets, or really changing much from the scouting and thinning role. Though most subs ended up as transports trying to keep the bypassed island garrisons alive. This also cut down on the IJN's effectiveness in sub warfare. As the war went on, the USN's institutional knowledge about sub warfare grew while Japan's shrank from disuse and inflexible doctrine.
The plan to bypass various bases was conceived in 1943 and it was just an attempt to cut down on Allied casualties, but it also had the unintended result of cutting deeply into Japan's offensive submarine capabilities.
Oh and figuring out how some subs were sunk is still a mystery. A lot of subs simply disappeared and nobody is sure what happened. The USS Hull was not credited with sinking a sub in 1945 when they made contact with a sub almost underneath them and dropped depth charges on it. Little debris was found. It was discovered post war that a transport sub was scheduled to pass through that area about that time and it never reported in after that day. There are many from the Hull who believed they sank that sub, but all we know for sure is that there was a sub in the area and it didn't report in after that day. The Hull probably sank it, but we will never know for sure.
There are a lot of sub losses with even fuzzier stories. All we know is they quit reporting in on a given day. Sometimes there was some ASW activity in the area, sometimes not. The losses to unknown causes list is fairly long.
Bill
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