NO. Army Regulation 670-1 specifies that only one badge from group one can be worn at a time. Group one consists of the EIB, CIB and CAB. Combat badges take precedence over skill badges. A soldier having earned both the EIB and CIB must wear the CIB. A soldier having earned both the CIB and CAB may choose which one to wear.
You can only wear one Type 1 skill badge, which is why you can't wear the CIB and EIB together. You can wear the CAB and CMB together (as the CMB is a Type 2 skill badge), but not the CAB and CIB. The only way you'd have been awarded both is to have been deployed and awarded one, then have reclassed to a different MOS and have been awarded the other on a separate deployment.
No.
Yes, you can wear a Combat Action Badge (CAB) and an Expert Infantryman Badge (EIB) on your Class A uniform. The regulations regarding the wear of these badges can be found in AR 670-1, paragraph 22-16 and 22-17.
You can only wear one at a time - they can't be worn together. With or without a CIB, the only way you'd be authorised to wear the EIB is if you've tested for and were awarded it. If you havn't done this, you can't wear the EIB, even if you have a CIB.
No. The only time this is done is a matter of local policy, where the unit might dictate that those who were awarded the EIB previously (and thus aren't testing for it) wear it during the period in which EIB testing is taking place.
Yes. The CAB (along with the CIB and EIB) is a Category 1 badge, of which only one may be worn. The CMB is a Category 2 badge, and can be worn along with a Category 1 badge.
The Marine Corps doesn't have an award which is equivalent to the Army's EIB. You'd have to hold an 11 or 18 series MOS while serving in the Army and pass the EIB testing in order to be eligible to wear it.
The EIB and the CIB are both military designations. When they have been earned, they can be worn. There is a limitation to the number of medals or ribbons that can be worn on a uniform.
No.
Technically, you have your own discretion to wear whichever one you choose. However, if you've been awarded a CIB, and choose instead to wear an EIB you've earned, you can expect your chain of command to not be particularly thrilled about it.
Yes, a non-infantry officer serving in an 11A slot, which is typically an infantry officer position, can wear the Expert Infantryman Badge (EIB) if they meet the required criteria and successfully complete the EIB testing. The EIB is open to personnel across various Army branches and is based on individual performance, not specific occupational specialties or positions.
Yes. It is a skill badge you were awarded, and you'll always be permitted to wear it, even if you don't remain in the infantry. Just like you would still wear jump wings if you were jump qualified, but serving in a leg unit. You don't lose your EIB simply for reclassing - however, you may have to fight to have the promotion points from your EIB counted at your promotion board, especially if you're going to a POG unit. Those promotion points are still valid, regardless of what MOS you hold at the time of your promotion board - don't forget that.
No. You have to either have an 11 series MOS at the time it was awarded or else reclass to an 11 series MOS afterwards in order to be able to wear it. You should be able to use it for promotion points, however.