Announced at the Brighton motorcycle show held during September 1965,[2] it was based on the earlier BSA Lightning with a power-upgrade achieved by higher compression-ratio 10.5:1 pistons and two large-bore Amal GP carburettors with velocity stacks [1] it was one of the first BSAs to have 12-volt electrics.

[4] The first A65S Spitfire of 1966 was confusingly designated Mark II and had a number of new features including two-way damped front forks, Girling shocks and a brace [1] between the downswept exhaust pipes.

[6] The bike was supplied as a sports-tourer with raised handlebar, forward-mounted rider footrests, a large dual seat with race-styled hump, and the glass-fibre fuel tank and side panels covering the oil tank/tool compartment and battery[1] were finished in Peony Red.

[citation needed] Keen to boost sales in the US market BSA produced a Spitfire with a two-gallon fuel tank following the trend set by the Harley Davidson Sportster.

Amal's Concentric carburetors were combined with twin-leading-shoe front brakes and independently adjustable Lucas ignition points for easier starting and tuning.