Instances where obsolete tank chassis are used to make quite modern vehicles that nevertheless remained experimental are common. Nearly a dozen German SPGs were produced in tiny amounts but still saw front line service. One common example is the Pz.Sfl.V tank destroyer, better known as the Sturer Emil. This vehicle was built on the chassis of the VK 30.01(H) heavy tank that was never put into mass production. Only two Pz.Sfl.V were built, but they were used quite successfully.
This German SPG was brought up as an example intentionally. Today it is displayed alongside its Soviet analogues, which also remained experimental. These are the SU-14-1 and T-100Y SPGs, built as bunker busters. They did not make it to the Winter War, but were likely used in battle during the defense of the NIBT Proving Grounds. Both vehicles were built on the chassis of tanks that were either considered obsolete or otherwise unfit.
