Recently, we have only mirrored engineer’s constructible weapons: AA gun, AT gun and MG nest. Addition of them, I suggest to add several unique things for each armies to make them more unique and make them interesting.
American: M18 recoilless rifle
It was 57mm caliber recoilless rifle used at the end of war. It can use HEAT, HE and Smoke (white phosphorus) shells. During the Pacific War, it was used to attack Japanese positions at the Battle of Okinawa.
At the European western front, this weapon deployed to frontline since March 1945 so it is delayed a bit. However, we already have several delayed weapons so I believe it is not a problem.
To differentiate from anti-tank guns, it would be good to add HE and Smoke shell instead of HEAT shells. It could be interesting weapon to provide supporting fire to infantry. Especially, white phosphorus shell would be useful.
M18 recoilless rifle on tripod
photo source
Japanese: Type 98 5 cm thrower / 九八式五糎投擲機
It was Bangalore torpedo thrower for engineers. It can use Type 99 Bangalore torpedo with wing and the explosive can with rod.
It has a variable amount of explosive, but explosive can can pack 2.7 - 7.2 kg of picric acid. Also, Type 99 torpedo had 2.25kg of RDX/TNT explosives.
It is a mortar so it had low mobility and it is difficult to aim quickly alike M18 recoilless rifle, but projectiles have large destructive power to destroy sandbags, barbed wires and infantry. However, it was designed to destroy obstructs so fragmentation power is inferior to other weapons.
photo of captured Type 98 5cm thrower with explosive can
photo source
German: SdKfz. 303 “Goliath”
It was German remote-controlled tracked mine used during WW2. Different to others, it is remote-controlled vehicle so it is impossible to reload next munitions and player who controlling this vehicle become defenseless.
You need to keep observing to steer, so you risk being shot, but being able to carry arbitrary bombs to remote locations can be very useful.
photo source
Soviet: Ampulomet
It was 125mm incendiary ampule launcher used since 1941. Its already exist in Stalingrad campaign.
It can launch incendiary ampule so it would be useful especially in urban warfare.
photo source
British: Northover Projector
It was British army and home guard’s substitute anti-tank gun / incendiary grenade launcher used during WW2. It may be somewhat silly to add but it would be interesting.
photo source
Italian: 7.5 cm Leichtgeschütz 40
It was German recoilless gun used during WW2. It was also used by Italian.