In possibly the second of the show's several properly dark episodes (The Battle of Godfrey's Cottage being the first), Mainwaring and Wilson contemplate the prospect of becoming the centre of a large crater.
Although it isn't strictly what we would now call a Bottle Episode, it perhaps influences the concept for future sitcoms by having the main characters stuck in place in bizarre circumstances.
Robert Dorning as the inspector is superbly officious, not quite grasping that if there were Germans coming out of Tmothy White's, some minor damage to the bank might not be high on anyone's list of worries.
The resolution is perhaps a slightly fluffed, with the bomb being lifted away so violently that our protagonsists would probably have been better just gently putting it down on the floor. Nevertheless, a solid classic.