The following is based on his patches from the first page of the scrapbook and from Combat Command A, 7th Armored Divsion, Records.

Robert D. Gruen was already a Lieutenant in the U.S. Army when the country entered World War II in December 1941 as a result of the attack on Pearl Harbor. The topmost patch on the first page of his scrapbook is that of the 64th Cavalry Division. The 64th was disbanded 30 Jan 1942, and he apparently was transferred 5 Feb 1942 to Fort Knox at the Armored Force Replacement Training Center, later known as the Armor School. There he may have briefly been in 3rd Armored Division and been one of the 3AD men who served as cadre in the formation of 7th Armored Division. He also has the patches of 1st Armored Division and 29th Infantry Division. It seems that he probably was transferred to these divisions after VE-Day as the point system led to men being transferred for determination of the order in which they were shipped back to stateside.

He began with 7th Armored Division in the Maintenance Company of the 40th Armored Regiment. This regiment was split up in the 30 Sep 1942 change of 7th Armored from a heavy armored division to a light armored division. It is not clear when he joined CCA Headquarters, where he was the S-4 Officer (Maintenance and Supply). He was promoted to Captain in Fall 1942. By October 1943, he held the rank of Major, which is the rank he retained for the duration of his time with 7th Armored Division.

The scrapbook, other than the first page, covers his time from Fort Knox through his return voyage home and ends with the menu for a post-war reunion that he and his wife hosted in 1946. It really is an exceptional record of one man's service that helps to illustrate aspects of the experiences of a great many others.