At the same time the O3U-3’s were ordered, 65 O3U-4’s were ordered to be powered by the larger hornet engine.  All of these aircraft were designated SU-2 or SU-3 since they were delivered to the Marines.  Forty-three became SU-2’s and 20 became SU-3’s.  The suffix number change indicated minor equipment changes.  One became the XSU-4, which differed from the others in cowling, cockpit and fin.  The SU-2’s and SU-3’s replaced the SU-1’s aboard the USS Lexington and USS Saratoga.  They served in various utility roles with Navy units.  Some were later made into SU-4’s.  As late as 1941 some of these aircraft were still stationed at various Navy Air Stations.