Expediency was a byword for the British motorcycle industry in the 1960s. When calls from the US demanded a superbike with around 44kW (60hp), Norton simply enlarged its existing twin to 750cc. Norton’s archrivals, Triumph and BSA, simply created a triple by adding another cylinder to their 500cc twin.

Although BSA and Triumph had existed under the same corporate umbrella from 1952, they had operated independently for more than a decade. BSA, or Birmingham Small Arms, was once the largest motorcycle manufacturer in Britain, most of them ‘bread and butter’ machines produced for the British Army and various police forces around the world.

Triumph, however, was more performance oriented, its Speed Twin establishing the parallel-twin layout as a new benchmark. When it came to creating a triple Triumph’s twin was chosen as the basis and much of the existing tooling retained. Instead of logically splitting the crankcase horizontally, the crankcase halves remained in a vertical plane, a centre section (with gearbox) flanked by two crankcase halves of the twin.

At the time a three-cylinder engine was quite unusual and at its heart was a forged crankshaft, initially reheated and twisted to provide the 120-degree throws. As with the Triumph twins there were two gear-driven camshafts fore and aft of the alloy block, with pushrods in tubes between the cylinders. The 67mm x 70mm bore and stroke provided 740cc and with a 9.5:1 compression ratio and three individual Amal 27mm carburettors, the power was 42.7kW (58hp) at 7250rpm.

Other features shared with the Triumph twins were dry sump lubrication, triplex chain primary drive, and a unit four-speed gearbox. Although the Triumph Trident and BSA Rocket 3 were ostensibly identical, the BSA carried its cylinder block at a slight forward inclination. The two versions also featured different frames, the Rocket 3 with a one-piece duplex cradle design and the Trident with a single-downtube Bonneville-type frame and bolted-on rear subframe. Both shared 19in wheels and drum brakes, although the front double leading shoe brake was stretched to the limit by the weight of 228kg and top speed of nearly 200km/h.

When it was initially released the triples were aimed squarely at the US market. Radical styling included ray-gun silencers, a bread-loaf fuel tank, and garish covers concealing the oil cooler. The Rocket 3 may have looked avant-garde, but it failed to win over the traditional clientele. In the face of the new Honda 750 Four the Rocket 3 was seen as a very conservative motorcycle with strong ties to the past. But the BSA Rocket 3 has undiminished appeal, symbolising the era when British motorcycles ruled the roost.

Ian's top 5 list: 1 Velocette Thruxton; 2 Vincent V-twin; 3 Triumph Bonneville; 4 Norton Commando; 5 BSA Rocket 3