The steelmaking furnaces were already available. For civilization in the One Piece World to have developed this far, some things were indispensable.
Like the steelmaking furnaces before them.
These furnaces had originally been used to produce iron billets for making muskets. The muskets of this world had clearly evolved from bronze firearms into iron firearms. As everyone knew, iron could not withstand the high temperatures of gunpowder. After one shot, the barrel would deform; the second shot would cause it to burst. Only steel could endure the heat of gunpowder.
Perhaps this was technology discarded by the World Government. Perhaps it was technology that cunning merchants had bought from the Celestial Dragons. In any case, it existed.
Steel bars smelted in blast furnaces were not especially useful, because at most they could be used to make steel blades. In naval battles, steel blades were the most useless weapons—bar none.
Even if one wanted to make gun barrels, powerful drill bits would still be needed.
Only gun barrels drilled by such bits spinning rapidly and evenly could qualify as proper barrels—though they might need tempering as well.
But these steel bars were indeed completely unsuitable.
The steel strips Leo wanted were slightly thinner than musket barrels, but they needed to be extremely long. They directly drew a thirty-meter-long strip from molten steel. Such a strip was thin but long, and it could be made because processing the enormous tree trunks in the One Piece World required steel saw blades that were just as long and thin. But this was merely a steel strip, not a saw blade, which made it rather strange.
And a thirty-meter-long steel strip... what was he planning to make?
Using this steel strip as the center, huge pieces of canvas were cut and sewn onto it.
This