A simple piece of kit
The 81mm Mortar (the Granatwerfer 34) was designed by Rheinmetall, went into production in 1934 and was used throughout the war with relatively little modification. I think it's fair to say the Mortar is a fairly simple weapon and the design was so elementary it was incredibly similar to the American M1 81mm mortar which saw service in WWII right up to the '50s. I found a great little training manual for US troops which illustrated the similarity perfectly describing to the US serviceman how anyone familiar with the M1 could operate the German equivalent easily, should they capture one and need to use it.
Over 75,000 of these were manufactured so they can often be found in museum displays and I have even seen them for sale at historical reenactment events. I'm not sure if my long-suffering wife would approve if I lugged one of these home.