>
>cut down in defeat by an ungracious victor - I-401 and
>her sister ships were surrendered to the US Navy at the end of World
>War II. The Navy's response to being handed the largest,
>longest-range submarines in the world was to take them out and sink
>them for target practice. This pathetically wasteful display of
>vindictiveness wasn't limited to Japanese hardware, either; most of
>Germany's U-boats, some of them the most advanced seagoing vessels
>ever constructed to that time, were taken out into the Atlantic and
>scuttled in an orgy of wanton pettiness codenamed Operation DEADLIGHT.
>

The scuttling of the I series of subs was to keep the technology from the Soviets. (who were demanding access to the subs per the terms of various treaties)

Take a look:
* https://www.stripes.com/news/researchers-unravel-the-mystery-of-japan-s-400-foot-aircraft-launching-submarine-1.258067
* https://ww2db.com/ship_spec.php?ship_id=453

(note: while it makes sense, I haven't dug too far down the resource tree to verify the articles -- but it lines up with everything I remember hearing about those subs)

Now, an idea for an alt-history book might involve a re-telling of the 'The Hunt for the Red October' but alas, we didn't have Tom Clancy back in the day to squirrel them away in a sleepy Maine river...