Step 8 should have been simple but I forgot to see what I had missed in the instructions.

The four Browning .303 machine guns had to be inserted in four little holes which were not wide enough.

I had taken about 30 minutes to try to fit them. Having done so I proceeded with installing parts B7 and B8 which did not seem to fit. It was obvious that I had inserted the machine guns 180 degrees due to combat fatigue!
I had to become a brain surgeon to fix this. I then glued B7 and B8 which were hard to insert. It was only then that I noticed how these parts were protruding.

I should have remembered to look at this photo.

That should teach me a lesson.