Beyond having its internals tweaked for supersonic operations, the RM8 featured some major additions to the JT8D’s baseline design that were specifically suited for the Viggen’s mission set. A large afterburner can was attached to the end of the engine, this massively increased thrust, but also turned the engines miserly fuel consumption into a gas guzzler when it was activated. The second was the addition of a set of thrust reverser petals housed inside the engine’s exhaust nozzle, along with perimeter bypass veins that would allow air to exit in a forward direction when the reversers were activated.

Few engine options were available that could satisfy such demanding specs. Turbofans were just emerging as the next great thing in aerospace propulsion technology. SAAB ended up with a license-built version of the Pratt & Whitney JT8D—the same engine flown on the 727 and DC-9 airliners—known locally as the Volvo RM8.

In the early 1960s while turbojets still filled the sky SAAB designers pursued a turbofan engine for their new multi-role fighter-attack-reconnaissance-interceptor. The type even had a maritime patrol variant. It was a broad mandate: The requirements for what became the Viggen dictated that the jet be capable of Mach two at high altitude and Mach one at sea level, all while possessing very good short takeoff and landing capabilities with good fuel efficiency at low and medium altitudes.

Sweden has built some fascinating aircraft over the years, but the SAAB 37 Viggen has to be one of the most interesting. The jet was unique—its delta-canard configuration was cutting-edge, and its ability to operate in austere conditions made it quite independent compared to most other western fighters of the era. The Saab's unique engine choice not only resulted in its stout appearance, and also gave it unique performance characteristics—especially when it came to short field operations.

The RM8B blasted out an incredible 28,100lbs of thrust in afterburner and 16,200lbs of ‘dry’ thrust without. To give you an idea of just how powerful the engine was for a fighter of the day, the popular General Electric J79 turbojet which powered the F-4 Phantom and F-104 Starfighter put out between 16,000lbs and 18,000lbs depending on the variant. The Pratt & Whitney F100 that would equip the state-of-the-art F-15A/B years after the Viggen first flew put out about 24,000lbs of thrust.

Teijo Hakala/wikicommons The Viggen trainer—this one a SK37E electronic warfare trainer aircraft—was especially cool looking with its staggered cockpit layout.

For what the Viggen gained in thrust with its RM8, it lost in sleekness. The large diameter engine necessitated a thick fuselage, but area-rule was still applied to the design to give it better supersonic capabilities than otherwise. With the jet’s fixed inlet design, it was never meant to be the fastest aircraft in the air anyway. The Viggen’s unique powerplant was paired with very tough landing gear—four wheels for the mains and two for the nose gear—and a unique vortex generating “double delta’ canard design, with flaps making up the trailing edge of the canards. All this added up to a marvelous short-field performer, with the Viggen being able to get airborne in less than 1,500 feet and become agile at low speeds right after liftoff.

Rune Rydh/wikicommons An impressive lineup of Viggens.