Upon first sight of the steel monster charging out of the alley, Roland could roughly guess what it was.
This wasn't a result of clairvoyant superpowers, nor did he have a spy network infiltrated into the Wehrmacht's R&D facilities, and it definitely wasn't due to imaginative powers so strong they defied the heavens. It was just exceptional observation skills, simple logical reasoning, combined with a bit of intelligence integration.
When he was still a cadet at the Alfheim Military Academy for Youths, the instructors devoted a considerable portion of their teaching to mobile warfare, annihilation warfare, and blitzkrieg, with relatively less on defensive operations. This focus was not only due to an emphasis on "offensive spirit" but largely because the Elf Camp wasn't adept at attrition warfare, hence their strategy aimed at swift victory to avoid protracted battles as much as possible.
