The man-rated Titan II was a liquid-propelled rocket, and consisted of two stages. The first stage was powered by an LR87 engine (although this engine has two combustion chambers and nozzles, it is considered a single unit because both chambers use common turbomachinery), and the second stage was propelled by an LR91 engine.
The rockets were purpose-built for the Gemini launches and featured some modifications compared to the Titan missiles. A malfunction detection system was installed to inform the crew of the rocket's status, and improve response in an emergency. Redundant systems were fitted to reduce the chances of launch failures. The Titan II promised greater reliability than the Atlas because of its hypergolically-fueled engines requiring far fewer components, however various dangers remained, such as the possibility of a guidance malfunction causing the engine nozzles to gimbal hard right/left. For this reason, an extra backup guidance system was added. The second stage propellant tanks were lengthened for longer burn time and unnecessary vernier engines and retro-rockets were removed. Because the second stage engine had had issues with combustion instability, it was equipped with baffled injectors. A radio control system replaced the inertial guidance used on the missiles, and modifications were made to the tracking, electrical and hydraulics systems in the interest of improved reliability. Modifications were overseen by the Air Force Systems Command. Aerojet, the manufacturer of the Titan's engines, had released a revised model during mid-1963 due to deficiencies in the original design and also attempting to improve manufacturing procedures.
Assembly was done at Martin-Marietta's Baltimore plant so as not to interfere with missile work at the Denver facility, although it also saved the former from a planned shutdown.