Thanks all for your replies - much appreciated.
Understand it now - it was all in the game guide but didn`t go into my head.... The Mobhack link helped as well - thanks for that.
Guess most of it is using the right tool for the job - experience matters.
As Gila states "click and pray"!
I have developed a hatred for 40mm AA guns.....
Learning to slowly probe to find them and stick as much artillery on them as I can.
Also - for any others learning the game like me - try and get to a big a map size as possible. This gives much more freedom for "invention & manoeuvre". This helped me with the learning curve. (slightly off-post!)