if you're familiar with world war ii the chances are you're familiar with the battle of the atlantic germany's attempts to suffocate the allied war effort with u-boat submarines attacking merchant shipping it was one of the key battles of the war but it wasn't the most successful submarine campaign on the other side of the world in the pacific the american navy was in its own little-known battle against japanese merchant shipping would prove to be utterly devastating to the imperial war effort [Music] in the years leading up to 1941 the u.s navy did not intend for submarines to form the backbone of a war against japanese merchant shipping in fact in 1930 the u.s had joined with britain in calling for submarines to be banned under the first london naval treaty this proposal never made it into international law but american disdain for using submarines to attack civilian shipping was real and was a long way from the us navy's thoughts in the 1930s that's not to say they didn't plan on using submarines though as the prospect of war with japan came into focus in the late 1930s and early 1940s construction of submarines was stepped up but the new american boats like the gato and balau classes weren't designed for attacking merchant ships necessarily designated as fleet submarines these boats were more than twice the size of their german counterparts and designed to carry a larger number of torpedoes and operate at greater range in order to attack enemy warships both the us and british navies did plan to interdict japanese shipping and blockade the home islands but with surface ships operating from ford bases at hong kong and manila not with submarines but on december 7th 1941 there was a change of plan just four hours after japan attacked pearl harbor admiral harold stark chief of naval operations ordered the u.s navy to execute unrestricted air and submarine warfare against japan the empire of japan's war economy in 1941 was incredibly vulnerable to the disruption of its shipping perhaps even more so than britain's even before the offensives to malaya the philippines and the duchy's indies began japan's merchant fleet was already burdened with carrying troops and supplies to and from china and filling the needs of much of its civilian economy after almost all of southeast asia fell to japan in 1942 it had access to all the raw materials it and its war economy could ever need but the iron ore bauxite rubber and oil still needed to be transported back to japan to be useful troops aircraft ammunition and weapons had to flow in the other direction to defend what it had taken and a huge amount of shipping had to flow through a single area between china and the philippines cut this route off and you might be able to strangle japan's war economy into submission that's the theory but in 1942 it was a distant prospect and did not rank as the us navy's top priority pacific submarines under rear admirals thomas withers and then robert english were given a wide variety of tasks in support of surface forces boats were sent to lay mines conduct reconnaissance collect weather data and deliver suppliers to beleaguered land positions amongst other things a lot of patrol time was also given over to trying to intercept and sink japanese warships their original purpose these attacks were rarely successful warships were fast and hard for a submarine to catch and engage of 23 contacts of japanese capital ships in 1942 only four resulted in damage to the enemy with none sunk in fact japan's submarines did a better job on this front they managed to sink the carriers yorktown and wasp and heavily damaged the battleship north carolina and aircraft carrier saratoga when not tasked to other activities american submarines carried out good old-fashioned commerce raiding across the western pacific sinking in 1942 274 merchant ships or at least that's what was claimed at the time in the heat of battle the size of ships could easily be inflated along with the number that was sunk a post-war report by the joint army navy assessment committee in 1947 put the figure for this year at 154 merchant ships sunk aircraft mines and other losses accounted for a further 87 ships either way it was not a strong performance for these submarines especially when compared to german u-boats which in the first half of 1942 alone had sunk 526 allied ships in the atlantic the reasons for this under performance were varied and not unconnected to the loss of submarine bases at the philippines and guam as part of a year in which the u.s was in retreat but problems specific to the submarine service ran deeper than that starting with their equipment the standard weapon for american submarines in 1942 was the mark 14 torpedo which had been developed in the 1920s and was untested in combat at the start of the war almost as soon as the fighting began doubt emerged over its reliability with numerous boats reporting that it failed to explode correctly as an example shortly before christmas 1941 the uss sargo fired eight torpedoes at four different targets and got no hits suspecting something was wrong the boat skipper lieutenant commander tyrell and dwight jacobs then spent almost an hour precisely tracking a new target on december 26th every measurement was double and triple checked and the boat closed to within a thousand yards of the target before firing four torpedoes all of them failed to explode now mark 14 torpedoes have two methods of detonation by contact with a ship or a magnetic detonator which would be triggered as the torpedo passed underneath one it would later emerge that both of these were defective though the navy was slow to acknowledge it and even slower to fix it by the time 1942 ended no live tests of a torpedo had taken place and the subs would enter 1943 still with temperamental torpedoes the american submarine fleet also experienced problems with its officers both sub-captains that weren't aggressive enough and a top brash that the naval historian clay blair argues failed to put a coherent plan together instead he says boats were too often shunted about willy-nilly on missions for which they were not suited blair argues that the submarine force should have been overwhelmingly focused on interdicting japanese merchant shipping particularly in the key area northwest of the philippines he recorded that the 54 war patrols mounted into this region were responsible for 81 sinkings more than 40 percent of the total for the year it was a pattern that rear admiral charles lockwood in command of these submarines based at pearl harbor learned from in 1943 some 50 percent of the patrols from hawaii were directed to this key zone compared to just 15 in 1942 lockwood himself was promoted to overall commander pacific submarines in february after the incumbent bob english and several other naval officers were killed in a plane crash lockwood oversaw a better but still inconsistent year for the submarine fleet 335 japanese ships were sunk by submarines with 135 more added from other causes it was a big rise on the previous year and enough to start to have an impact on the imperial economy imports of key raw materials including coal iron bauxite and rice fell to 16.4 million tons down from more than 20 million tons the previous year the americans were aided through 1943 by better availability of torpedoes as the supply shortages that have plagued the previous year began to ease but though they had more torpedoes the mark 14 was still not reliable though more effort was put into fixing the issues as the year wore on all of the defects were eventually solved by september 1943 22 months after the war had begun the improved fortunes of allied submarines in 1943 did not escape the attention of the imperial japanese navy towards the end of the year the japanese finally set up a dedicated force to protect its merchant shipping the merchant escort command under admiral kashiroykawa japan entered world war ii without an effective idea of how to protect its merchant shipping commerce defence during a protracted grueling war had not formed a central part of a naval strategy which emphasized fighting a single decisive battle to emerge victorious as such the resources that abram lacava was able to command to protect japan's vital shipping were meager at best of the 69 destroyers that japan possessed at the outbreak of war 38 have been sunk by the end of 1943 so there was precious little to work with several classes of small escort ships were ordered a bit like the flower class corvettes of the royal navy but most of these were not complete until the latter half of the war the japanese also ramped up construction of fresh merchant ships to replace those being lost more than a million tons of shipping would be constructed between april 1943 and april 1944 joined by increasing numbers of escorts as the new year approached but unfortunately for japan it would not be enough to prevent what was coming by the start of 1944 the united states navy's pacific submarines were reaching a very high level of efficiency problems with crews and torpedoes had largely been worked out a developed system of wolf packs have been implemented with multiple boats coordinating attacks together superior radar technology had been installed on many boats and detailed information on japanese movements was provided by ultra decrypts from bletchley park through 1944 the subs demonstrated their effectiveness against japanese warships they sank one battleship seven aircraft carriers two heavy cruisers seven light cruisers and 30 destroyers to this formidable force was added the key ingredient of new air and sea bases on the mariana islands of saipan and guam captured in mid-1944 the mariana islands provided a staging base for naval and air forces that was dramatically closer to japan's key shipping lanes than pearl harbor was the impact on japan's shipping was even more devastating than on its warships from submarines alone 548 merchant ships were destroyed another 432 sunk by other allied combat units mostly carrier and land-based aircraft which could now range deep into the east china sea it was a devastating assault that only got worse as the year drew on in the final months of 1944 u.s forces began to recapture the philippines with american forces now based so close the supply route to japan northwest of luzon then became almost completely severed and the ability of japan to transport vital oil virtually stopped dead japanese imports for 1944 collapsed to 10 million tons half the value it was two years before the size of the empire's merchant fleet went the same way halving from 4.1 to just 2 million tons the impact on japan's war economy was profound production of steel and aluminium fell off a cliff and the military stockpile of vital aviation fuel dropped to critical levels by early 1945 effectively no oil was getting through to the home islands which meant a critical shortage of fuel to the point where the japanese government began trying to extract oil from pine needles in other words according to the historian phillips and o'brien by the time the us air force was even thinking about firebombing major japanese cities japanese production was already in a state of terminal collapse as their ability to move raw materials and finished goods around their empire had ground to a halt it was nothing short of the total strangulation of a war economy by air and sea to such an extent that the submarine force actually had a quieter year in 1945 sinking only 160 ships or so this was largely because what remained of japan's merchant marine was bottled up in port almost not daring to leave and being sunk anyway in large numbers by aircraft and particularly by mines which were dropped outside harbor entrances across the war as a whole japan lost more than nine million tons of shipping of which more than six million was sunk after the start of 1944 it was an extraordinary success and one of the most important victories of the pacific war with their war economy in ruins the fighting of 1944 and 45 became an increasingly uphill fight for the japanese army and navy for example shortages of fuel because tankers were getting sunk meant training for new japanese pilots was continually scaled back throughout the war scale back training meant inexperienced pilots getting massacred in the skies above the philippine sea in what became known to the us as the marianas turkey shoot however important as it was the battle against japanese merchant shipping is also one of the least known battles of the second world war unlike their german counterparts the exploits of u.s submarines were usually secret and not reported at the time and in the years since the war's end historians and the public have often chosen to focus more on big decisive moments midway lady golf okinawa iwo jima but perhaps the most decisive battle of them all was one that went on quietly under the waves and in the sky over the pacific and brought the japanese war economy to its knees next time we're going to tell the story of one small part of this decisive battle the story of commander law sunramaj's 48-minute rampage through a japanese convoy in the summer of 1944 make sure to subscribe and hit the notification bell so you don't miss it you