The most significant difference between the SR.53 and SR.177 was the latter's use of a jet engine with nearly five times the thrust of the one adopted for the former. While the SR.53 had relied mostly on its rocket engine for climbing, the SR.177 would be able to add considerable endurance by conserving use of its rocket for the dash towards a target only. It was expected that the added endurance would allow the SR.177 to perform roles other than pure interception; these roles were expected to include strike and reconnaissance missions. The SR.53 design had been considerably enlarged to accommodate the new engine, and the original sleek lines were forfeited for the chin-mounted air intake.