Caduceus saluted formally. No melta... Flamers would be the best way though the tunnels. He would have to talk to the devastator captains of course, but flamers seemed to the the way forward to deal with this threat. If their hides were so thick that even the holy promethium could no pierce it, then they would need to bring heavy bolters. Plasma would likely be just as disastrous if used in such close quaters- the blast might reflect off the walls, melt through the rock and bring it down, or a misfire would leave the marine carrying the weapon, and his fellows, fodder for the apothecary. 

Vehicles would also be useless... Perhaps he might beseech one of the dreadnoughts? No, they should not be woken from their slumber for such a petty campaign. "I have much to do Lord Commander. I bid you good day." He half-bowed and left. No need to anger the man more than his so-called insubordination already had, the Servitors winking off, the holograms maintained by them vanishing in a blink of static. "01110111 01100001 01110010." The simple chant he murmured to himself helped keep his mind sharp as he walked, his tongue wandering familiarly over the words. He had turned his vox box off so that nobody else might hear the chant, the forgemaster returning to whence he came from.

The forge was grand. The chant of the omnissiah flooded his ears as he entered, the few techmarines that were in the room saluting as he walked past in reverence. He placed his chainaxe up onto the wall and bowed his head in respect, before taking off his robes, and subsequently his armour, leaving him naked bar for the black carapace. He quickly rectified this by donning his robes once more, and walking purposefully towards a small side room.

Instructing the servitor to let none enter unless it was an emergency, Cadeucus shut the door behind him and looked around the room, before sitting cross-legged on the floor. He must beseech the omnissiah to find the clear way ahead for the machines. Perhaps after this a visit to the chaplain might be in order.

"The flesh is weak. The metal is willing."