Accounts compare the M.20's performance with that of Battle of Britain aircraft. The M.20 (345mph at 20,400ft) was powered by a Rolls-Royce Merlin XX with a two‑speed supercharger. A Hurricane IIB with the same engine did 342mph at 22,000ft. A Spitfire VC, powered by a similar Merlin 45 did 374mph at 13,000ft. The Spitfire was armed with two 20mm cannons and four .303 machine guns. The other two aircraft were armed with eight .303 machine guns. All these figures are from the same reference.