— Official game quote
The German Assault Pioneer is a feared enemy support unit and is armed with powerful MP-40 SMG. Pioneer squads were considered reliable, high-quality and no-fail teams during WW2. He can defuse your mines and TNT destroy your defences with TNT charges and defuse duds. They are even more dangerous due to the fact, that they tend to pin down people in bunkers and wound/kill people later during the game. If 3 multiple pioneers appear on the battlefield at the same time, they become automatic fire suppressors and pinning or killing everything that is standing up and firing at them.
If he plants a TNT charge, send your engineer to get it. If your engineer manages to defuse it, you get free TNT charge and your engineer gets some XP! You can get revenge on Assault Pioneers who defuse your explosives by booby-trapping them them, which blows up the pioneer as he attempts to defuse it. If you kill 25 of these guys with booby taps, you get a useful ribbon. He is German version of engineer without construction capabilities, other than a TNT charge.