The US was never remotely close to equal, much less superior to the IJN in torpedoes. The best that can really be said about American torpedoes is that they were acceptable by the end of the war and finally exploded when they were supposed to more often than not.
The Mark 15 torpedo, the torpedo used by USN surface ships throughout the war could either travel 4,500 yards at 45 knots or 14,000 yards at 26.5 knots with a 363kg warhead. The IJN Type 93 Long Lance could travel either 24,000 yards at 50 knots, or 44,000 yards at 36 knots with a 490kg warhead. Air and submarine launched torpedo differences were similar, if not quite as dramatic between the USN and IJN. And yes, if you’re familiar with just how unbelievably unreliable the USN Mark 14 submarine torpedo was for the first half of the war, the Mark 15 surface and Mark 13 air dropped torpedo suffered the exact same problems as the Mark 14
The Mark 15 had the same basic design problems that plagued the Mark 14 for the first 20 months following U.S. entry into the war, though this was not realized nearly as quickly by the destroyer crews as it was by the submariners. One major shared deficiency was the Mark 6 exploder, which usually caused duds.[1] Another was a tendency to run deeper than set, often missing the target.[3] Surface-combatant torpedo attacks very often included confusing splashes from gunnery and aerial bombs, obscuring smoke screens, and quick maneuvering to evade counterattack. Rarely was a destroyer given a chance for a slow, careful surprise attack. Torpedo results were difficult to estimate under these circumstances. The correction of the Mark 15’s problems would depend on the submariners solving theirs.[4] Another problem with early war-built Mark 15s was the substitution of zinc for cadmium as interior plating for air flask sections and water compartments, due to a wartime shortage of cadmium. This resulted in zinc oxide clogging water strainers, leading to erratic runs and engine failures. After the failure of corrosion inhibition efforts, the ultimate solution was to re-coat the areas with cadmium or phenolic resin (Heresite).[3] The final straw for Admiral Chester W. Nimitz (CINCPOA) to begin to resolve this problem that other admirals and torpedo manufacturers kept claiming was not a design problem but due to the performance of the submariners and surface ships’ crew was when a submarine fleet successfully infiltrated Tokyo Harbor on 11 June 1943 but not a single torpedo that was launched by them hit any Japanese ships. The issues with the Mark 14 and Mark 15 torpedoes were not completely fixed until November 1943 when Vice Admiral Thomas C. Kinkaid (Seventh Fleet, SWPA) overruled Rear Admiral Ralph Waldo Christie, who refused to believe that his torpedoes had malfunctions, and ordered all submarine and destroyer captains to disable their faulty magnetic detonators and also the contact pin problem was finally resolved that same month.
One of the major advantages that the IJN enjoyed early in the war in night engagements wasn’t just superior night optics and searchlights, but that they had trained heavily for night engagements by their light forces as part of their decisive battle doctrine, imagining the naval war to be decided by one giant engagement of the respective battlelines. Japan was going to be inferior in numbers of battleships, so attritting the US battleline with submarine and nighttime surface torpedo attacks was heavily planned and practiced as part of their basic doctrine. The USN did contemplate night actions, but largely gave actual training, planning and doctrine for it lip service.
It should also be noted that while the US used surface torpedoes almost exclusively on destroyers, full torpedo batteries were standard on both light and heavy Japanese cruisers. IJN heavy cruisers like the Takao-class carried 16 24inch Long Lance tubes along with 10 8" naval rifles. No USN heavy cruiser carried any torpedoes. Oh, and the Japanese also carried reloads, often a full set, for their torpedo tubes on their surface ships. The USN didn’t carry reloads for torpedoes on their surface ships.
One disadvantage that all of this emphasis on torpedo tactics designed against the US surface fleet by the IJN that should be mentioned is that Japanese submarine doctrine was to use lines of submarines to locate and attack battle elements of the US surface fleet. This was also part of US practice, but only part. The US was much more interested in using fleet submarines for commerce raiding, which Japan almost entirely ignored doing for the entire duration of the war. This led to some amazing successes - the I-19 fired what is regarded as the single most successful torpedo salvo of the war, sinking its target the carrier USS Wasp with 3 of the 6 torpedoes while
The remaining three torpedoes travelled for another 5 miles into the path of the Hornet task force. The spread hit the U.S. battleship North Carolina on its port side and the destroyer O’Brien, the latter of which later sank on 19 October 1942 en route for repairs. North Carolina sustained significant damage and underwent repairs at Pearl Harbor until 16 November 1942.
I-19’s torpedo salvo sank an aircraft carrier and a destroyer and severely damaged a battleship, making it one of the most damaging torpedo salvos in history.
US submarine torpedoes couldn’t even have travelled far enough to reach the second US task group. However, these successes were few and far between, while the US submarine fleet eventually crippled the entire Japanese economy - albeit only once their torpedoes started to actually work after 2 years.