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According to Parshall & Tully's Shattered Sword, the four Japanese aircraft carriers lost at the Battle of Midway (1942) carried both high and normal octane aviation fuel. Does anyone here know why?

Logistics would suggest that it's best to carry as few types of fuel as possible.

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    $\begingroup$ Well, the war was largely about access to oil, so high octane fuel was likely in short supply-- perhaps some aircraft had engines that could use lower octane w/ minimal degradation in performance -- or perhaps lower octane fuel was carried aboard the carrier as a "reserve" in case the higher-octane fuel was exhausted -- read more about the development of various grades of aviation gasoline here en.m.wikipedia.org/wiki/Gasoline $\endgroup$ Sep 27 '21 at 5:53
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    $\begingroup$ (Begging the question, did some of the carrier aircraft carry two different types of fuel simultaneously -- ) $\endgroup$ Sep 27 '21 at 11:56
  • $\begingroup$ @quietflyer an engine can't run on lower octane fuel than designed for, and it won't get any benefit from running on higher octane fuel then designed for, so there is no reason to switch fuels in flight. $\endgroup$
    – Jan Hudec
    Oct 2 '21 at 19:03
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The logical answer is that there were aircraft that required both low octane fuel and high octane fuel on board. You don't want to use high octane fuel in a low octane engine (unless you're forced to; the low octane engine can't scavenge the excess lead in the high octane fuel and it fouls plugs among other things) and vice versa (the high octane engine blows up from detonation if using low octane fuel). Either there were Japanese patrol or utility aircraft on board used a lower octane fuel than the fighters and torpedo bombers, or the ships had gasoline powered engines aboard used for other things like standby power and required a separate lower octane fuel supply.

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  • $\begingroup$ They had three main types. The Zero, Val, and Kate, plus Soryu carried a pair of Judy prototypes. $\endgroup$
    – Davidw
    Oct 2 '21 at 19:51
  • $\begingroup$ But according to Wikipedia at any rate they all used 92 octane engines. I suspect there there was just avgas and automotive type gas for stationary motors or towing equipment. $\endgroup$
    – John K
    Oct 3 '21 at 15:42

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