Final answer:
The USS New York (LPD-21)'s bow stem was constructed with 7 1/2 tons of steel from the World Trade Center.
Step-by-step explanation:
The ship's bow stem that was constructed from 7 1/2 tons of steel from the World Trade Center is the USS New York (LPD-21). This was a symbolic act of tribute to the victims of the September 11 attacks. The steel from the World Trade Center was melted down and used in the construction of the ship, making it a significant piece of naval engineering and a moving memorial.