Let's face it, when a nation or in FL's case, a House is staring down the barrel history has shown that morals and scientific limitations can and should go right out the window in order to save themselves.
With that in mind, what kind of weapon would you envisage the Houses pulling out of the hat to either turn the tide of their bad fortunes, or just as a weapon of deterrent?
Here is my idea for a 'secret weapon' for Bretonia:
Hammer of Carina
As you can probably guess by the name, the weapon is in itself a very powerful Ion or rapid plasma weapon. I considered a Gauss weapon, but that doesn't have enough punch.
The Hammer of Carina uses technology replicated from the Liberty Siege Cruiser's chassis and energy amplification system, only the Bretonians in their traditional 'bodge job' ethos with working with what they have and overworking it, have created a cannon nearly doubling in size of the Liberty Siege Cruiser itself. It is in itself a daunting weapon to behold, if it could have engines to propel itself, it would be classified as a Super Capital Destroyer. The primary debilitating factor of this weapon is that it is a mostly immobile orbital weapon platform designed solely to defend the capital of Bretonia, New London from orbit.
Unfortunately, construction of the Hammer of Carina kept hitting delay upon delay and the weapon still resides inside the restricted Bretonian systems. However, it is operational, and any ship caught withing its system stretching range, is almost certainly going to be smashed down to the molecular level. Each shot depletes the same amount of power as it takes to fuel a Battleship for three operational months. Therefore logistics are a crippling problem of this system.
I, kinda over-thought/overwrote that. But I love the thought of Bretonia holding a 'super artillery' unit in orbit of the yet unseen Bretonian 4.86 system, ready to annihilate any enemies of the crown.