Iron Clads- Battle ships that had iron plating;
The Gatling gun- could fire 600 round a minuets; and
The rifle- the first drilled bore gun that was designed to curve the bullet and fire mini balls that expanded as the went through the barrel.
Also, the extensive use of torpedoes. And even the birth of the submarine for sea battles along with the revolving turret used on monitor style battle ships. Balloons were also used for reconnaissance.