Why did the US Navy and Marine Corps use satanic symbolism in WW2?

Fully realizing that it is probably a major faux pas to return to a topic long years after answers, including my own, have been posted, but while looking for something else altogether I stumbled across this passage and thought it germane, contemporary writing on creation of the Carrier Air Group 84 insignia found on page 7 of the VF-84 War History.

“After canvasing the squadron for ideas for a squadron insigne an agreement was reached with the bombing and torpedo squadrons for a group insignia. The use of a common background and similar central figure in these insignia stress the group rather than the individual squadron. It is the belief that each squadron while excelling in its own weapon has individual limitations. Working as part of a coordinated group, however they become invincible. Each squadron is represented by a black wolf armed with its primary weapon and superimposed on a devils head. The wolf is vicious and bloodthirsty, though retaining fully his predatory cunning. This is indicative of the aggressive manner in which this group will wreak carnage on our country’s enemies. In folklore, the werewolf was a normal person suddenly turned into a beast who retained his human intelligence.
“Similarly, the pilots of this group will be changed when they scent the enemy. The devil in the background watching the destruction is turning green with envy. The Air Group will be known as ‘WOLF GANG’ and ‘THE UNHOLY THREE’. The battle cry is ‘LOOK OUT BELOW!’”

Sample of the VT-84, Torpedo Squadron 84, of Air Group 84

The wonders of the enthusiastic imagination.

Why did the US Navy and Marine Corps use satanic symbolism in WW2?

I believe the "evil" symbolism serves a purpose (unlike what others implied), and it's not primarily to intimidate the enemy.

Few people realize this, but normal men do not naturally make good soldiers:

Grossman was committed to helping the U.S. military become more effective in fighting wars. He revealed that the Army has to train its members to kill because most people do not want to kill other human beings. He cited a study conducted by the Army after World War II that discovered that in combat only 15 to 20 percent of soldiers fired their weapons and an even smaller percentage fired to kill. The Army then changed its combat training to desensitize soldiers to the humanity of the enemy. The new training was effective, and as a result, 55 percent of the infantrymen in the Korean War fired their weapons, and 90 to 95 percent fired them in Vietnam.

Being an effective soldier has a lot to do with overcoming one's natural morality, and much of military training, and possibly titles like "son of Satan" help reinforce that.

                               A Picture's Worth A Thousand Words...

Why did the US Navy and Marine Corps use satanic symbolism in WW2?

Ultimately for the same reason it's still using it today; as such, the real question would be why not?

[T]he U.S. was largely [a] Christian country at that time.

Which would probably explain why they heavily employed Christian symbolism associated with the notions of bad or evil to begin with; after all, Satan and his devils are characters appearing within Judaeo-Christian scriptures, are they not?

As for why one would employ such symbolism in the first place, R Leonard's very first sentence pretty much sums it up: the rebelliousness of youth, rebels or daredevils being regarded as bad boys by the various authorities they rebelled against, and Satan or the devil being the ultimate embodiment of bad or evil within the cultural milieu those young men were raised in; in German, for instance, the term Satansbraten (literally, Satan's brat) is used to denote a similar concept.

I don't think that Japanese cared too much

The Japanese had several divisions named after ferocious predators or mythical beasts (bear, dragon, eagle, panther, tiger, whale, wolf), and four others named after wrath, fury, thunder, and destruction, whose onomastic symbolism, needless to say, served a similar purpose.

Young men full of piss and vinegar trying to sound fierce and scary or just different. Christianity had absolutely nothing to do with it any more than some perceived Satanic leanings.

What about VF-31 "the Flying Meataxers" . . . shall we worry for the knife-making industry?

The original Helldiver was a biplane dive bomber in the 1930's, the SBC, named by the manufacturer, Curtiss Aircraft. All Curtiss dive bombers thereafter retained the moniker.

How about VF-11, the Sun Downers. Full disclosure, my father designed their insignia (see my avatar). A red sun setting in the ocean being shot down by two F4F fighters. Obviously the symbolism of shooting down the Japanese sun, but also in the sailing navy, sun downers were a crew that worked beyond when the sun passed the yardarm and thus did not splice the main-brace until just about sundown . . . implying a hard working crew that kept at it as long as there was light.

How about VF-42, they didn’t even have a name, but their insignia dated back to the early 1920’s when it was a float-plane scout squadron with a goose wearing a flight helmet and googles striding along with pontoons on his feet . . . that’s scary.

Worried about Hellcats? That plane’s predecessor was the F4F Wildcat, its successor was the F8F Bearcat and let us not forget the concurrent F7F Tigercat . . . traditionally Grumman fighter type aircraft were XXXXcat . . . with a slight break for F9F Panthers and such, the last Grumman fighter in service was the F-14 Tomcat. Oh, and I’d point out that one definition of Hellcat is a bad-tempered, spiteful, woman; a shrew, though it could also be complimentary in the right context. Also a mythical being that haunts certain southern swamplands and northern woods.

And the USN officially began assigning names to its aircraft in October 1941, generally keeping what came unofficially before, but retaining the right to name aircraft, rather than letting the manufacturers make the call.

This becomes a question of just how much one wants to read into, or parse out of, an aircraft's or unit’s nickname.

Let’s see . . . going through Barrett Tillman’s US Navy Fighter Squadrons in World War II (Specialty Press, 1997), where he mentions a named nickname/moniker or where I can throw some light . . .

VF-1 ‘High Hatters;’ VF-2 (the first one) ‘Flying Chiefs’ (which refers to Chief Petty Officers as the squadron rank and file pilots were largely enlisted Naval Aviation Pilots); VF-2 (the second one) ‘Rippers,’ later ‘Tall Dogs;’ VF-3 not really named after him, but sported a insignia showing Felix the Cat carrying a bomb; VF-4 ‘Red Rippers,’ (and, no, ‘red’ had nothing to do with Satan, it was a large tusked hogshead; VBF-6 ‘Whistling Death; VF-9 (1st-3d tours) ‘Cat o’ Nines,’ (4th tour) ‘Hellcats;’ VF-10 ‘Grim Reapers;’ VF-11 ‘Sun Downers;’ VF-12 ‘Corsairs’ later ‘Thunderbirds;’ VF-13 ‘Black Cats;’ VF-14 ‘Iron Angels;’ VF-15 ‘Fighting Aces;’ VF-16 ‘Pistol Packin’ Airdales;’ VF-17 ‘Jolly Rogers;’ VF-19 ‘Satan’s Kittens;’ VF-31 ‘Flying Meataxers;’ VF-32 ‘Outlaw’s Bandits’ (Eddie Outlaw was the squadron commander); VF-40 ‘Flying Boars;’ VF-41 (an earlier incarnation of VF-4, above, also ‘Red Rippers;’ VF-44 ‘Crusaders’ a nice Christian moniker, eh; VF-46 ‘Men-O-War;’ VF-47 ‘Fighting Cocks;’ VF-49 ‘Forty Niners;’ VF-50 ‘Devil Cats;’ VF(N)-53 AND VF(N)-63 ‘Sleepless Knights” ("(N)” denotes a night unit); VF-72 ‘Fighting Wasps;’ VF-74 ‘Flying Wolfhounds;’ VF-80 ‘Vorse’s Vipers” (Albert Vorse was the 1st of 3 squadron commanders); VF-81 ‘Freelancers;’ VF-83 ‘Kangaroos;’ VF-85 ‘Sky Pirates;' VF-86 ‘Wild Hares;’ VBF-86 ‘Vapor Trails;’ VF-88 ‘Gamec**ks;’ VBF-88 ‘Gringos;’ and lastly VF(N)-90 ‘Bats’.

I could go through the same exercise with VB, VT, and VP/VPB squadrons and probably the Marines as well, but I’ll refrain. Interested parties can count up the suspected Satanic type messages in the above squadron nicknames as opposed to the humorous, say ‘Wild Hares’ or even the angelic, ‘Iron Angels.’ My count is three, four at a stretch, out of some 40 squadrons or squadron nicknames listed might use words associated with the dark side.

I’d point out that Jim Flatley, the first commander of VF-10, came up with the ‘Grim Reapers’ nickname was a devout Catholic. I’d also suggest his thinking on such matters was not atypical of the times. He wrote of his thoughts and words to his pilots on the eve of VF-10’s entry into combat in October 1942 to which I commend to your reading, see Stanley Johnson, The Grim Reapers, Dutton and Company, 1943, pages 121-123.

So, what is the worry about, what, less than 10% of the squadron names found and noted, hardly what one might term "heavily loaded". I’d suggest that this was a typical rate. And this is evidence of a tilt towards Satanism and away from Christianity just, how? Further, the 21st century tendency to parse every word of the past for criticism never crossed the minds of anyone in the 1940’s. No offense was intended, none should be found.

And does anyone want to tackle the USAAF unit nicknames?

Also, there was no VF-191 in WW2, you perhaps mean the WW2 era designation VF-19; likewise there was no VMA-241, that squadron is a lineal from VMSB-241 of the WW2 era.