Wikipedia

https://www.military.com/history/why-us-navy-operated-fleet-of-ice-cream-ships-during-world-war-ii.html

The U.S. Navy had (in)famously outlawed alcohol aboard ships in 1914, six years before Prohibition, but it still needed to fill the gap in morale boosting power a sailors daily drink left behind. As any noncommissioned officer who has overseen junior enlisted Americans will tell you: if you don't give them something to boost their morale, they can get into anything ... and you might not like what they find.

Luckily, they found ice cream. Airmen in the Army Air Forces were using open seats on B-17 Flying Fortresses as ice-cream freezers during bombing missions (where temperatures could be as low as -25°F). Navy and Marine Corps aviators would mix canned milk and cocoa powder in fuel drop tanks, then fly missions, returning to their otherwise tropical or desert climates with tanks full of sweet treats.

After an assistant to then-Under Secretary of the Navy James Forrestal wrote that "ice cream, in my opinion, has been the most neglected of all the important morale factors," the secretary made getting ice cream to those troops his highest priority. Thereafter, any ship large enough would be fitted with a so-called "gedunk bar" (gedunk being the World War II sailor's word for ice cream, but now just means any junk food). The ice cream had the triple benefit of providing calories, helping beat the heat and boosting morale.

Funderburg writes that by February 1945, at the same time the Allies were preparing to invade Germany in earnest, the Army began building ice-cream factories to bring half-pint cartons "right into the foxholes."

https://www.thefoodhistorian.com/blog/world-war-wednesday-ice-cream-is-a-fighting-food

By the Second World War, ice cream was firmly entrenched aboard Naval vessels. So much so, that battleships and aircraft carriers were actually outfitted with ice cream machinery, and by the end of the war the Navy was training sailors in their uses through special classes.

https://www.thestar.com.my/news/true-or-not/2023/11/03/quickcheck-did-a-submarine039s-crew-steal-a-battleship039s-ice-cream-maker

QuickCheck: Did a submarine's crew steal a battleship's ice cream maker?

Yes, this really happened when the US Navy submarine USS Tang was docked in San Francisco at the same time the battleship USS Tennessee was also in port.

As explained in the Unauthorized History of the Pacific War Podcast by The National WWII Museum staff historian Seth Paridon, ice cream machines were generally only carried by ships like battleships, aircraft carriers, and heavy cruisers with one or more ice cream machines on board.

Paridon then said that the Tang's skipper - then-Lieutenant Commander Richard O'Kane – gave an order to the sub's Chief of the Boat, William F. Ballinger, to “go find me an ice-cream maker, by hook or by crook and get it installed aboard this submarine.”

“Ballinger went and 'liberated' the ice cream maker aboard the battleship Tennessee that was tied up in San Francisco at that time, and literally just a couple of hours after Tang had shoved off, the shore patrol showed up looking for their ice cream maker that was now aboard a submarine,” he said.

https://www.wearethemighty.com/mighty-trending/navy-tradition-ice-cream-pilots/

The Navy tradition that rewards ice cream for rescued pilots

Imagine you’re a Navy torpedo pilot in World War II. Your life is exciting, your job is essential to American security and victory, but you spend most days crammed into a metal matchbox filled with gas, strapped with explosives, and flying over shark-filled waters of crushing depths. But your Navy wants to get you back if you ever go down, so it came up with a novel way of rescuing you: ice cream bounties.

So, carrier crews came up with a silly but effective way of rewarding boat crews and those of smaller ships for helping their downed pilots out: If they brought a pilot back to the carrier, the carrier would give them gallons of ice cream and potentially some extra goodies like a bottle or two of spirits.

The exact amount of ice cream transferred was different for different carriers, and it seems to have changed over time. But Daniel W. Klohs was a sailor on the USS Hancock in World War II, and he remembered being on the bridge the first time a destroyer brought back a pilot:

I told the captain (Hickey) that it was customary to award the DD with 25 gallons of ice cream for the crew and two bottles of whiskey for the Capt. and Exec. We ended up giving 30 gallons of ice cream because it was packed in 10-gallon containers. This set a new precedent for the return of aviators.