A Titan II nuclear missile in its silo at the Titan II museum near Tucson, Arizona (http://www.pimaair.org/tmm/).
The Titan was a spin-off from the Atlas Missile Program. The Atlas was a single stage missile essentially consisting of a fuel tank, a guidance equipment, a warhead on the nose and engines at the rear.
In contrast, the Titan was a two stage missile. Each of the two stages carried liquid oxygen and rocket propulsion fuel. The most notable difference between the Titan I and Titan II was the type of oxidizer and propellant each used. Titan I used liquid oxygen as an oxidizer. It was cryogenic, meaning it had to be kept at an extremely low temperature, generally around-1950C. It had to be stored in special refrigerated tanks and pumped aboard the missile before it was fired. Liquid oxygen is extremely volatile, inflammable, and very difficult to handle, especially within the confines of an enclosed missile silo.