 Early on even the low-powered versions of the engine were considered unusable because of reliability problems.The A3D would prove successful with alternate engines, but the F3H-1 was relegated to subsonic performance using the lower-powered engine and continued to be subsonic even after substitution of the higher-power Allison J71.It has been stated, that although considered failures, the F3H-1 could have been competitive with early supersonic Air Force's Century Series fighters had the original engines delivered on their design specifications.