Warbreakers - MacGuffin ideas

After talking with Alan, he suggested that I need to decide what the "ominous rumours" from the Austrian Alps actually are, on the basis that this will help inform the design work.  Since the idea is that the "rumours" are a way for the central powers to win the war, the ideas will fall into 2 categories - superweapon, and technical breakthrough.

Superweapon ideas

• Giant supergun able to shell London and force the british to surrender.
• Massive zepplin aircraft carrier able to launch devastating airstrikes.
• Superheavy mobile battlefortress that will be able to single-handedly defeat the british army.
• Superheavy artillery to pound the british trenches into oblivion. 
• Cruise Missiles
• Mechs

Technical Breakthrough ideas

• Atom bomb
• Super-armour (something like titanium, to make personal body armour practical again)
• Directed-Radiation weaponry (Radium-based death rays)
• Practical Military Rockets
• High-capacity electricity storage devices (supercapacitors?)
• Lightning guns
• Contact neurotoxic gasses
• A Superexplosive
• Computer
• Submunition Artillery Shells
• Napalm
• Cold Fusion
• Practical Exoskeleton

Now I just need to choose one, preferably one that hasn't been done to death...