The most decorated unit in the U.S. military were... Japanese 

100th Battalion, 442nd Infantry - made up entirely of 'Nesei' (2nd generation Japanese-Americans), even as the U.S. held thousands of Japanese, including their family members, in interment camps.

 "One Puka Puka" - 100th Infantry  (The "Hawaiian Provisional Battalion")

The 100th/442 fought in Italy, southern France, and Germany, in some tough campaigns including the rescue of the "Lost Battalion" (141st Regiment), and even captured a German Submarine!  In all, 9,486 Purple Hearts were issued (many earning double and triples), and the official casualty rate, as a fraction of all who served, is 93%.  It was awarded 7 Presidential Unit Citations, 4,000 Bronze Stars, 1,200 Oak Leaf Clusters added to the Bronze Star, 560 Silver Stars, 28 Oak Leaf Clusters to the Silver Star, 52 Distinguished Service Crosses, 15 battlefield commissions, and more than 20 soldiers were awarded the Medal of Honor.



In 1942, more than 1/3 of the population of Hawaii was of Japanese descent. So its not surprising that the state's National Guard and "Hawaii Territorial Guard" also included large numbers of Japanese-Americans.  After the bombing of Pearl Harbor, the War Department called for the removal of all soldiers of Japanese ancestry from active service.  However, the Army General in Hawaii decided to keep about 1,300 Japanese from the National Guard, who performed so well in training that the U.S. reversed its decision on Japanese Americans serving in the armed forces and formed the 442nd Infantry Regimental Combat Team, with 14,000 Japanese-Americans serving during the course of the war.

The 'Stars and Stripes' newspaper cartoonist Bill Mauldin, said, "No combat unit in the Army could exceed [them] in loyalty, hard work, courage and sacrifice. Hardly a man of them hasn't been decorated at least twice, and their casualty lists were appalling.... A lot of us in Italy used to scratch our heads and wonder how we would feel if we were wearing the uniform of a country that mistreated our families. Most of us came to the conclusion that we would be pretty damn sulky about it, and we marveled at those guys who didn't sulk ... and showed more character and guts per man than any 10 of the rest of us ... . We were proud to be wearing the same uniform."

The 442nd is also nicknamed "The Purple Heart Battalion"

Sgt Goichi Suehiro, Weapons Platoon (4th) machine gun squad leader.
St. Die Area, France, 13 Nov 1944