BMW has just launched an M4 CSL for the 2023 model year, the first car to wear those famous three letters since the legendary E46-generation M3 CSL built between 2002 and 2004.

If you’re unfamiliar with the famous badge, CSL first featured on the 3.0 CSL race car of the 1970s and has traditionally stood for “Coupe, Sport, Lightweight.” It marks the most track-focused cars offered by BMW, as far as road cars are concerned, and as you'll soon find out, BMW looked at using the badge on more than just coupes.

It turns out the automaker multiple times in the past came close to launching CSL models, as the video below reveals. It's part one of a two-part series and shows us some secret CSL prototypes, including CSL versions of the M6 coupe and M5 sedan, as well as a V-8 version of the previous M3 CSL.

The M3 CSL with the V-8 is based on the E46 M3 CSL that BMW originally offered with an inline-6. The V-8 here was borrowed from the E39-generation M5 on sale at the time, a 4.9-liter V-8.

The M5 CSL was an even wilder idea. It is based on the E60-generation M5 and featured a tuned version of that car's 5.0-liter V-10. It also featured a dual-clutch transmission instead of the finicky automated manual the stock M5 came with.

As for the M6 CSL, it is based on the E63-generation M6 coupe and was probably the closest of the three prototypes to get to production. The global financial crisis happened during the car's development, making the business case for such a high-end model hard to justify. It features active aerodynamics (mostly under its floor) coupled with an uprated V-10.

Naturally, each of the prototypes also feature extensive weight savings.

Stay tuned for part two of the series which details a secret M2 CSL prototype that was developed.