Would Americans be neutral towards The Battle at Dunkirk?

No. The withdrawal of British forces allowed for the invasion of France, a serious roadblock to victory that the Americans later invested and lost many lives in undoing. The victory of the British at Dunkirk greatly diminished Nazi forces, but their subsequent withdrawal led to serious future problems. Thus, Americans would support a British victory and a British occupation, not a British loss. Dunkuirk was not really a battle, it was the place in France where most of the British army escaped from to England. At that time America was not involved in WWII (not until Pearl Harbour, Dec 1941) and could easily have decided to remain neutral, though possibly friendly towards Britainh rather than Germany. There were some in the USA at that time who thought Britain was finished and that a humiliating peace with Nazi Germany would be the best outcome. One such was Edward Kennedy Snr, father of the three Kennedy brothers. Correction: The father of the 3 Kennedy brothers was Joseph P. Kennedy.