Axis & Allies Developer and Playtester; War of the Ring Editor and Playtester
Let's say that Picardy is contested between France and Germany. Then British infantry which begin the turn in Brest move in to Picardy, are the British infantry forced to do one round of combat with the German units or can they choose not to engage like say French units moving in to the contested area would have been able to ?
Attacking would be optional. Attacking is only mandatory when you move units into a territory that is either hostile or neutral (not contested).
Also let's begin with the same scenario but this time British infantry are being transported from London to Picardy, are they forced to engage ?
No. That would be an amphibious reinforcement.
If they aren't forced to engage then can the German artillery still fire on them because they are doing an amphibious landing (if the original answer is that the British infantry aren't forced to engage) ?
No. Artillery may only make pre-emptive strikes against units making an amphibious assault (moving into a hostile or neutral territory).
Also can the British do a naval bombardment but still not have their infantry engage the Germans (assuming again that the original answer is that the British infantry aren't forced to engage) ?
No. Battleships may bombard only in support of an amphibious assault (moving into a hostile or neutral territory).
Lastly, let's keep the original scenario; Picardy being contested by France and Germany. And for some reason, France have infantry in London and also they have a battleship and transport in sea zone 9 and they transport their infantry in to contested Picardy but they do not want to engage the Germans in combat this turn. Can they do a naval bombardment even though they don't want to fight the Germans on land ? Also let's say the French don't want to engage the Germans, can the German artillery still fire on the French infantry that did an amphibious landing ?
No. See above.