(only an atomic bomb would have helped them)
...and a delivery system. If the German's had had an A-bomb, there weren't a whole lot of options available to them to use it. They had no planes with the capability to delivery it from both a payload and range standpoint...except on the drawing board. Short of sticking it in a sub for a one way mission, the US mainland or UK islands wouldn't have much to worry about. For front line use I guess they could have used a truck to drive near a target.
The Great Depression keeps getting overlooked. The Brit's and many other countries had weapons systems that could
have been developed between the wars, but no way of funding them. Without the urgency of WW2, it would have taken forever to get the Garand into service in any real numbers. The UK had one of the world's most advanced mechanized forces post WW1, in both tactics and equipment, but the Great Depression helped change that.