Marines from Battery B, Battalion Landing Team 3/5, 15th Marine Expeditionary Unit, lift weights inside one of three fitness rooms aboard the USS Rushmore, Aug. 18. Marines from the MEU exercise regularly during the unit?s final training evolution, Certification Exercise. CERTEX differs from previous exercises because Marines and Sailors react to unknown scenarios using the Marine Corps? Rapid Response Planning Process. - Marines from Battery B, Battalion Landing Team 3/5, 15th Marine Expeditionary Unit, lift weights inside one of three fitness rooms aboard the USS Rushmore, Aug. 18. Marines from the MEU exercise regularly during the unit?s final training evolution, Certification Exercise. CERTEX differs from previous exercises because Marines and Sailors react to unknown scenarios using the Marine Corps? Rapid Response Planning Process.