For the little story ...
At the beginning of XIX century, the kingdom of Piedmont-Sardinia decides the construction of a set of fortification to prevent a possible French invasion, the Barrière de l'Esseillon.
Between 1830 and 1860, five forts were built on the site of Esseillon, Fort Charles-Félix was built between Fort Marie-Christine and Fort Victor-Emmanuel. It is not the most imposing but the only one that was built as a "star". When Savoy was annexed to France, the fort was partly destroyed by French artillery to "honour" the terms of the contract to destroy the forts... but the French, conscious of the strategic interest of the forts, did not do it. And thanks to the progress of the artillery, Fort Charles Félix lost all usefulness
In 1860, the annexation of Savoy to France, then the breakthrough of the Frejus rail tunnel (commissioned in 1871) completely changed the strategic data: the forts lose their usefulness and will have then only a limited utility .
I suggest you making a voucher in alternative past, in which after X events, the French troops find themselves blocked at the foot of the barrier of Esseillon. with no other choice but to assault the fort in very rough weather conditions... Having very few artillery, the French troops will have other choices only to attack the garrison in the bayonet ....
To succeed in taking the fort, you have a few pieces of artillery and some mortars. Unfortunately, the fort was built in such a way that it will be very difficult to breach. The only way to catch him is to launch a frontal assault through either the door or the ladders
This is a first version, bugs and balancing concerns may remain, don’t hesitate to let me know them