With the Viggen, Sweden introduced the first onboard computer with integrated circuits. The CK37 changed the pilot-machine relationship forever.
In summary
In the early 1960s, while the United States and the USSR dominated military aviation, Sweden took a quiet but decisive lead. With the Saab JA37 Viggen program, Stockholm was not only focusing on aerodynamics and engine power. The real technological leap was hidden in the cockpit. The CK37, the Viggen’s central computer, became the world’s first onboard computer to use integrated circuits. With just 25 kilobytes of memory, it managed navigation, ballistic calculations, landing assistance, and radar coordination. This feat was not based on raw power, but on a highly efficient software architecture and a human-machine interface designed for a single pilot. The Viggen thus ushered in the era of the digital cockpit. Later, the transition to the CD 107, derived from American Singer-Kearfott technologies, confirmed this conceptual advance. The history of the CK37 is not anecdotal. It explains why Sweden beat the major powers in the field of onboard computing.
The strategic context that necessitated the digital revolution
Sweden made a unique choice during the Cold War. Non-aligned but exposed, it had to be able to defend its territory on its own. This required aircraft capable of operating from road bases, with few personnel, in a very short time. The pilot had to take off, navigate, intercept, and return without heavy assistance.
This structural constraint pushed Saab to seek a radical solution. Increasing the number of crew members was not an option. The answer lay in intelligent automation. The computer became a digital teammate.
The CK37, a computer ahead of its time
The Central Kalkylator 37 was not just a navigation computer. It was designed to be the brain of the combat system. Its most striking feature was the use of integrated circuits, whereas most Western aeronautical computers still used discrete transistors.
This decision reduced weight and power consumption and improved reliability. The CK37 weighed about 20 kilograms, a remarkable figure for the time. Its total memory was about 25 kilobytes, which seems insignificant today, but required extreme rigor in software design.
How 25 kilobytes are enough to fly an entire mission
The CK37 operates according to a logic of priorities. Each critical function has dedicated memory space and guaranteed processor time. There is nothing superfluous.
Optimized inertial navigation
The computer receives data from a simplified inertial unit. It continuously calculates position, speed, and heading. Errors are corrected by recalibration points entered manually by the pilot. This system allows for autonomous navigation, even in a jammed environment.
Real-time ballistic calculation
For ground attacks, the CK37 calculates the release parameters based on speed, altitude, and flight profile. The pilot no longer has to make estimates. The computer displays a firing solution that can be used immediately.
Air interception support
During fighter missions, the CK37 works with the onboard radar. It provides guidance and anticipates trajectories. The pilot receives concise information without cognitive overload.
Landing assistance on dispersed bases
One of the most impressive functions is road landing. The CK37 calculates the descent parameters and guides the pilot to a short area, sometimes less than 800 meters. This capability is essential to the Swedish doctrine of dispersion.
A revolutionary human-machine interface
The real innovation of the CK37 is not just computer-based. It is ergonomic. Saab understood early on that the value of a computer depends on how the pilot interacts with it.
The single-pilot concept
The Viggen is designed so that a single pilot can perform the roles of pilot and navigator.
The CK37 filters information. It only shows what is necessary at that precise moment. This philosophy contrasts sharply with the dials-saturated cockpits of the 1960s.
Mode selectors and contextual logic
The pilot selects simple modes: navigation, attack, interception, return. The CK37 automatically adapts its calculations and displays. This logic drastically reduces mental load.
The precursor to the digital cockpit
Even without modern screens, the Viggen anticipates the glass cockpit. Essential data is centralized. The pilot no longer “reads” isolated instruments. He follows coherent information.
Why Sweden was ahead of the United States and the USSR
In the United States, on-board computers exist, but they are often specialized. In the USSR, aeronautical computing is progressing more slowly and remains compartmentalized. The CK37, on the other hand, is integrated from the outset as the heart of the system.
Sweden also has a cultural advantage. Teams are small and decision cycles are short. Saab can experiment, correct, and integrate quickly. This agility explains its technological lead.
The accepted limitations of the CK37
The CK37 is not perfect. Its limited memory requires compromises. Software updates are complex. Any new function requires the removal or optimization of another. There is no room for improvisation.
But this constraint becomes a strength. Every line of code is useful. Every function is tested to the extreme. The reliability of the system in operation is high, which counts for more than theoretical sophistication.
The transition to the CD 107 in the JA37
With the arrival of the JA37 version, dedicated to fighter aircraft, the Viggen evolved. The CK37 gave way to the more powerful CD 107. This evolution was based on American-licensed technologies, notably from the work of Singer-Kearfott and its SKC-2037 computer.
Increased power, but an unchanged philosophy
The CD 107 offered more memory and computing speed. It enabled better radar integration and increased interception capabilities. However, the philosophy remained the same. Priority was given to operational efficiency and ergonomics.
Successful technological hybridization
Contrary to popular belief, the adoption of American technologies did not mark a step backwards. It demonstrated Saab’s ability to integrate foreign components into an already mature architecture. The Viggen remains a coherent system.
The legacy of the CK37 in modern aviation
The influence of the CK37 extends far beyond the Viggen. It established the idea that software is a weapon. This vision was taken up in subsequent programs, including the Gripen, where computing became central.
Today, fighter aircraft have gigabytes of memory and massively parallel processors. Yet the logic remains the same: filter, prioritize, assist the pilot without overwhelming them. This approach was born with the CK37.
A lesson in technological restraint
The CK37 reminds us of an often-forgotten truth. Superiority does not always come from brute force. Sometimes it comes from conceptual discipline. In 1967, Sweden had neither the American budgets nor the Soviet resources. It compensated with system intelligence.
The Viggen is not just an aircraft. It is a manifesto. A manifesto for aviation where the machine works for man, not the other way around. The CK37, with its 25 kilobytes, paved the way for digital air warfare long before the term existed.
Sources
- Saab Aircraft Archives, Viggen and CK37 programs
- Swedish Air Force historical technical manuals
- Jane’s Avionics and Aircraft Systems, 1970s–1980s editions
- Technical analyses of the evolution of European onboard computers
- Comparative studies on Cold War aeronautical computing
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