What does decimated[ refer to, the Japanese or the US?

[v0031]

Battle of Midway - June 1942

Midway was a catastrophic defeat from which the Imperial Japanese Navy never fully recovered. Much of the credit goes to the codebreakers who revealed the Japanese plan to ambush U.S. forces in time for the Allies to plan a counter-ambush.
The Japanese plan to split American forces also failed. The U.S. then launched a major air assault on the Japanese carriers. The TBF Avenger torpedo bombers were intercepted by Japanese Zeroes and decimated, but the SBD Dauntless dive bombers attacking afterwards got through. They arrived just as the Japanese planes were refuelling and rearming on deck. Three of four Japanese carriers were destroyed, tilting the course of the war against Japan.

[v0031]

Battle of Stalingrad - August 1942 to February 1943

In contrast to the great sweeping tank battles elsewhere on the Eastern Front, Stalingrad was protracted and bloody urban warfare fought from street to street, house to house, and room to room as the Red Army resisted German attempts to take the city. Russia's defenses were based on thousands of strongpoints, each manned by an infantry squad, in apartments, office buildings, and factories, all with strict orders forbidding retreat.
German artillery and airpower virtually demolished the city but failed to dislodge the defenders. Eventually the German force was itself surrounded. The total number of casualties may have been as many as two million including civilians.

Whose casualties?

[dead0man]

Battle of Midway - June 1942

Midway was a catastrophic defeat from which the Imperial Japanese Navy never fully recovered. Much of the credit goes to the codebreakers who revealed the Japanese plan to ambush U.S. forces in time for the Allies to plan a counter-ambush.
The Japanese plan to split American forces also failed. The U.S. then launched a major air assault on the Japanese carriers. The TBF Avenger torpedo bombers were intercepted by Japanese Zeroes and decimated, but the SBD Dauntless dive bombers attacking afterwards got through. They arrived just as the Japanese planes were refuelling and rearming on deck. Three of four Japanese carriers were destroyed, tilting the course of the war against Japan.

The Zeroes shot down most of the first wave (the Avengers).  Decimated technically/traditionlly only means 1 in 10 were killed, but the word just means "destroyed" more or less now.

as for the second one, total causalities on both sides, including civies.