Harmon, Frank Maxwell Andrews, Simon Bolivar Buckner, Jr. and Lesley J. McNair, all lieutenant generals at the time of their deaths, were the highest-ranking Americans to die in World War II. Harmon and Andrews were killed in plane crashes. McNair was killed by friendly fire (position bombed by allied planes at the beginning of the Normandy breakout). Buckner was the only one killed by enemy action.
Seventh Army Lt. Gen. Alexander Patch died in November 1945 (he was then in the US as commander of the 4th Army).
Third Army Lt. Gen. George Patton died December 1945 in a traffic accident (he then was commanding the Fifteenth United States Army based in Bad Nauheim). He had been promoted to 4 star general on April 14, 1945.
I learned several other things in looking this stuff up.
11 generals were promoted from 3 stars to 4 stars between March 5 and April 15, 1945. That is about 5% of all generals ever promoted to 4 stars. Before WW II there had only been 10 active generals promoted to 4 stars so this was almost doubling that count. Three: Eisenhower, Hap Arnold and Joseph Stillwell had been promoted in 1943 and 1944.
Although the rank of Lieutenant is below the rank of Major, the rank of Lieutenant General is above the rank of Major General. The reference to this did not explain why.
General Stilwell and Admiral McCain also died shortly after the war. Stilwell in 1946 and McCain just a few days after the Japanese surrender.
Think of these three ranks: Captain, Colonel, General. They each need an assistant, someone to "act in their place": a "lieu-tenant." So, we have a Lieutenant standing in for a Captain, a Lt. Colonel in lieu of a full Colonel, and a Lt. Gen. acting for a full General.
"Major," according to them, derives from the antiquated "Sergeant Major," and would be an even more junior assistant: a Sgt. Maj. reporting to a Lt., a Major to a Lt. Col., and a Major Gen. to a Lt. Gen.