How to find out what someone did to receive the bronze star in Worls War II?

Its probably not going to be easy. The Bronze Star could be awarded for either valor, or "meritorious service". If the award was for valor, the medal came with a small bronze "V device" to be worn on the ribbon of the Medal.

Any citation for valor was accompanied by a citation, a written statement of what the soldier did to earn his medal. A copy of this was placed in the soldier's personnel file. 90% of WWII personnel files burned up in a fire in the warehouse in St. Louis, where the government had them stored, in 1973. You might get lucky and the file of the soldier you are interested in might be unburned. You can obtain a copy from the National Archives. Go to for details.

Another copy of the citation would be retained in the papers of the soldier's unit. These are also in the National Archives, but you would almost certainly have to visit the records repository in Suitland, Maryland and ferret this out yourself.

To keep up morale on the homefront the Army (and other service branches) had public relations specialists. These individuals stayed busy sending "good news" back to the hometown newspapers of the soldiers in the news, including usually sending a copy of Medal citations to the decorated soldier's hometown paper. If you know where the soldier was from, and are there yourself today, you could try the public library or the newspaper office and see if they have the war years of the paper on microfilm. Unless you can narrow down the time frame involved, this could take a long time, and you might be tempted to skim through and miss the citation. That is, if the newspaper printed it. Many, if not most newspapers did, though, word for word.

Another new army award for WWII was the Combat Infantryman's Badge (CIB). This is about four inches long and a half inch tall, a metal pin, with a blue enamel field with a rifle-musket on it. Its worn above the ribbons of all other medals, except that for the Medal of Honor. To get the CIB in WWII, you had to be an actual combat infantryman. Not just in an infantry division, but in one of the "letter" companies of the division which did the actual foot-soldier fighting. After the war was over the army decided that any man who earned the CIB in WWII was also entitled to the Bronze Star Medal. Most WWII civilian-soldiers were discharged by the time the army decided this, and many never knew of the decision or never bothered to write for their Medal. This mass awarding of the Bronze Star Medal was for "meritorious service", so, no "V device".