1. It is my understanding that division/unit patches were permitted on both shoulders....and that the left shoulder patch denoted 'current ' unit and the right shoulder patch denoted a soldiers's 'previous' unit. Is that correct? 2. I believe that a MOS 745 (Rifleman) was required to qualify for the CIB. If a soldier met that MOS requirement and engaged only in prisoner guard duty, could he be eligible for a CIB?
Does the definition of a "combat unit" apply to a Division as a whole or just certain units within a Division? If it is by Division, would it be possible for a soldier to be assigned to a unit (organically or by attachment or by some form of oversight) within a Division, but never personally engaged in direct combat and, thereby, still qualified to wear the patch of that Division on the right shoulder? AND, when is a designated combat unit no longer a combat unit? Sort of a complex question/scenario....hope it clear!
The US military also has a similar looking Combat Action Badge which has a knife & wreath. Not a WW2 era award of course.
It is complex. Not all patches were of divisions. Corps and Army also had patches and if a soldier was in a smaller unit (say, battalion or company level) that was attached directly to Army or Corps, he could wear those patches. Regiments could be independent, but were not authorized shoulder patches. I've never seen any that I can remember, anyway. They wore Distinctive Unit Insignia on the lower lapel of their Service Dress. There were not a lot of independent infantry regiments that saw combat, but there were a few, so it could be possible for a soldier to not have a shoulder patch for a unit he served with, if it was an independent regiment. Also, not all regiments had DUIs. Also common were non-divisional battalion-sized units. They were units like AAA or engineering and were often attached to "groups", which were then subordinate to Corps or Army. Such formations would often have no unit insignia, as none were ever authorized. They could wear Corps or Army patches, but it was not uncommon to see the formations shuttled around to different commands, so they may have never worn any.
My father was in an infantry regiment (473rd) that had an unofficial theater-made patch. It was worn under the 5th Army patch. You can see it in my avatar. I wish I had one. His unit was converted to infantry from a AAA unit, which was originally a CA unit. As far as I can tell, his unit never got a DUI, although he was awarded a CIB.
Wearing the SSI of a previous combat division is not something that was done in World War II or Korea and may have become habitual post Vietnam. The earliest version of AR 670-1 that I can find that describes the wearing of two patches is from 1992. IIRC, it was something that became habitual in the All-Volunteer Army during the 1970s. In World War II, the wearing of SSI was essentially unregulated and there was a proliferation of Army, Corps, Divisional, Branch, and other SSI that were non-reg. The SSI in World War II was habitually worn on the left shoulder. If a soldier was transferred to a unit with a different SSI he was expected to replace it with the new one on his uniform.
It varied by theater, but in the ETOUSA typically non-divisional units wore their Branch SSI if they had one. Eventually, units attached to divisions would often substitute or add the divisional SSI. In my Dad's case, he recalled when they landed on UTAH, the men in his battalion (537th AAA AW Bn, Mbl) wore the 'AA' Branch SSI, but then after some months of attachment to the 90th Inf Div when it was obvious such "attachment" was more or less permanent, they added the 'T/O' SSI. I suspect the same may have happened with the 712th Tk Bn and the 773d TD Bn, especially after the group affiliations for those units disappeared when the Armd and TD Gp HQ were re-rolled and lost the last of its tactical function. Yep. They typically wore an SSI patterned on its Branch insignia. AAA used the red, white, and blue 'AA' roundel, Engineers the 'Castle", Tankers the 'Armored Triangle', TD the 'Black Puma', and so on. Army and Corps SSI were typically only worn by assigned and attached HQ personnel. Attached units wore either the divisional SSI or the Branch SSI. However, there were all kind of variants, since the Army was not as hugely obsessed about uniform regulations in a combat zone then...well, Patton was, but that was a bit different.