I've known for ages that partisan cannons can be converted into smartcannons. However, I've just noticed that the partisan cannons are made by NAMI whereas the smartcannons are made by Rasiermeisser. This is a bit inconsistent, no?
By the way, I've been playing this game on-and-off for something like 4 years, and I've only just realised how good the smartcannons are! It's great how you can still discover new things