I believe there is a section of Mark Ragan's book which quotes an order from the CSA HQ in Shreveport to "strip the iron off the Signal and the Wave" for use on the subs. That could have been a lot of iron. When the wreck of the Ponchatrain was examined in Little Rock, it was estimated that 6 to 7 tons of iron were available, much of it in rr iron or boiler iron. Certainly enough to build small subs if you had the mechanics and the tools to do it. Still wondering how they thought subs would be useful in a riverine campaign. The manpowered subs didn't have the speed to attack a moving target and would be used against anchored or moored vessels. Perhaps they could have been used against static structures like bridges or wharf boats, but it seems like a lot of trouble for a small return.