A manga about combat maids engaging in trench warfare

August 1893, church calendar. The kingdom of Nohmaland declared war on the Flatanian empire and invaded their territory under the pretext of atrocities against Patlasi within the empire In order to support the regular troops, the empire send the [armed service], and armed maid group tasked with guarding/policing the castle inside, to the front lines. The war against the kingdom still continues.