Already fired and then defending in an assault

[clarkmj111]

so a German activated - and fired at an adjacent stack. disrupoted on targer NE on the other
German is marked moved/fired
US then activates and assaults the hex

I realise the rule says a unit defending in an assualt does not activate and is NOT marked with a fired/moved
but if the already fired do they get to fire again in the assualt?

In this instance its a German HMG
cant they use full fire when defending? and first fire (as dug in?0 or do the HMG restrictions apply when they are the assault defender?