With his AMR 33 not yet being delivered to the French army — this would happen in June 1934 — Louis Renault used two of the five AMR 33 prototypes to improve the type. In the middle of February 1934 he sent the first, N° 79759, to the testing commission, after it had from September 1933 been lengthened and refitted with a much more powerful Nerva Stella 28 CV engine, which now was placed in the back, instead of the front, of the vehicle, both to reduce the effect of engine noise as to attain a better weight distribution, two problems that had become apparent in 1933 when the prototypes had been used for manoeuvres. The exhaust pipe was placed at the back and the ventilator moved from the right to the left side. Renault was hesitant to introduce such expensive improvements in the production run; but in February 1934 the head of the French Cavalry, General Flavigny, insisted on these changes being made.