Guns attack with Hard Defence instead of Hard Attack?

[WarGamer1945]

My unit is the attacker and does an active attack on enemy unit..
Tested with regular and direct ranged attack.. Checking combat reports in detail and found out, that guns like 75mm german PAK or 88 attacks with hard defence instead of hard attack. Seems to be the case with any kind of gun. Tanks and other troop types attack with hard attack as it should be.
Can anyone clarify this please? Or which troop types behaves in this way?