The beginnings of the bkan 1 program
In the same 1949 army headquarters memo mentioned in the previous post, the army also saw the need for a 15 cm self-propelled autoloaded artillery gun (the 10,5 cm gun was intended for smaller formations, while the 15 cm SPG would be a division or corps-level asset). Development of this artillery piece was contracted to Bofors, with deliveries planned to start in spring 1956 (in reality, the production version of this SPG finally entered service in 1967, delayed over 10 years).
These documents describe the original intentions and requirements for the SPG, and a preliminary drawing is attached. It was originally intended to weigh 30 tons; the production version would eventually enter service weighing 52 tons. A large part of the increased weight was due to a requirement added later, namely that the entire fighting compartment and the external ammunition storage must be armor protected and sealed against NBC weapons.