This is a massive, stange, outlier in IBM's journey into portable personal computers. CL for 'Color Laptop' and 57 for....... fuck knows. The type is 8554 and it runs MCA bus. It's almost completely unique although it shares a look similar to that of the possibly-vaporware, Japan-only PS/55 Power (PC) Laptop EWS - which also feels like a skunkworks project.
Some sources state this machine started as a Model N27sx - a 'for fun' IBM Japan design for domestic japanese market. I can't find much source material that this is true though. Apparently, the CPU was downgraded from a 486 to a 386 so as to not compete with other PS/2 machines. Supposedly there are some hidden clues on the machines that despite it's international 85xx model designation, the plant ID is 97 which is IBM Japan Entry Systems factory in Fujisawa.
I need to go and re-read the All About Thinkpad book but there is at least a whole chapter about how the display inside the CL57 (10.4-inch TFT colour LCD with 640 x 480 VGA resolution) was so important to the success of the Thinkpad. From memory, it was first found in the CL57 (April 1992), the PS/2e (July 1993) and the 700C (October 1992) - with the far more portable notebook 700C having the most use for such a bright, sharp, high-referesh, low power, flat and portable display. These were jointly manufactered by IBM and Toshiba who agreed to split the purchase of the first production run 50/50 until IBM found they could sell almost all of them far easier than they thought.
Apparently, the reason the CL57 is so big is that the 10.4 inch TFT display still required a large powerful backlight, which meant the lid had to be huge. It appears later versions of the Toshiba-made TFT display became smaller, first seen in the C23V 'proper notebook' and then perfected in the C52/700C.
Here is a size comparison showing the 5523 PS/55 Note on the left and the CL57 on the right:
