Final answer:
Charlie is exploring technology as a lens, focusing on ironclads and their significant impact on naval warfare during the Civil War.
Step-by-step explanation:
Charlie is reading a book about ironclads and their role in revolutionizing naval warfare during the Civil War. The lens he is most likely exploring is technology. Ironclads were a new kind of military technology that represented a significant shift in naval strategy and capabilities. Similar to how railroads and steamboats revolutionized transportation and commerce during the period, ironclads changed the nature of naval engagement by introducing armored, steam-powered ships. These technological advancements underscore the transportation revolution and the transformative power of new technologies during this era.