Loading bombs- How?

[zeppelin]

I've read loads of threads here and elsewhere, but am unable to find the answer. I'm new at this so bear with me.

Just exactly how do get bombs in the bomb bay of the Heinkel ( or any other bomber)?
In FMB, under weapon sets, the machine guns are all shown with ammo but the bomb bay is empty. The only setting for the bombs is Default or Empty. The only drop down menu to mention bombs is in the detonator section. This doesn't get bombs loaded.

What am I missing?

Thanks in anticipation.