It is quite true that D-day was considered fairly risky — and due to the seasonal weather, had to be conducted before September of any year.

Churchill knew better than anyone the danger of getting thrown back into the sea after an invasion, for he had been the First Sea Lord and was the main proponent for what became the fiasco of Gallipoli in WWI (though it turns out that the admirals and captains refused to advance as aggressively as he demanded — they were afraid of the minefields). The failure at Gallipoli had cost 140K+ killed and wounded on the British and ANZAC side.

But Churchill was by nature a ballsy man, and did not allow what happened at Gallipoli stop him from aggressively pushing for offensive operations against German forces at sea and in the air even as the UK stood alone between the fall of France and Germany’s invasion of the USSR.