The main innovation of Isaac Peral's submarine was the inclusion of hidden weaponry, which earlier models did not have, as well as a system for launching torpedoes on the surface and under the water. Torpedoes are self-propelled, underwater projectiles that detonate when they get close to, or make contact with, a target. From the time of their invention in the 19th century, inventors and companies continued to develop different kinds of torpedo. The Peral carried Schwartzkopff torpedoes, produced by the company of the same name, which were made of brass and therefore less likely to corrode. It also carried Whitehead torpedoes, made of steel and driven by compressed air, which could reach speeds of between 8 and 10 knots.