First Lt. Stephen Black, operations officer, Headquarters Detachment, Combat Logistics Battalion 15, 15th Marine Expeditionary Unit, works out on a stationary bike inside one of three fitness rooms aboard the USS Rushmore, Aug. 18. Marines from the MEU exercise regularly during the unitâ€™s final training evolution, Certification Exercise. CERTEX differs from previous exercises because Marines and Sailors react to unknown scenarios using the Marine Corpsâ€™ Rapid Response Planning Process.