Let’s not mix up to two issues of spur gears vs helical; planetary vs non-planetary.  Note that most of those big WWII engines used planetary, but they used spur gears

Quite Right Al. Mistral's unit is a custom built spur gear planetary. Maybe a bit better than helical but much more expensive. Actually Helical allows greater tooth contact than a spur gear, but does have the disadvantage of thrust from the gearset. The submarine guys wanted quiet high power sets and started using herringbone or double mirrored teeth on a single gear, quiet with no thrusting.

Bill Jepson