The LR87 is a liquid rocket engine used on Titan II intercontinental ballistic missiles and space boosters. Though this powerful engine is in reality two engines working together, it is considered a single unit. The LR87 first flew in 1959.
The engine is a "fixed-thrust" engine -- it could not be throttled, and it is not restartable in flight. The LR87 delivered approximately 430,000 pounds of thrust using "hypergolic" fuel. Hypergolic fuels are liquids that ignite when mixed together. Late-model LR87s used Aerozine-50 nitrogen tetroxide, which are storable at room temperature and can remain in their tanks for long periods. This gave Titan II missiles quick-launch capability, an important feature for responding to a threat. Early LR87 models used super-chilled liquid oxygen and kerosene, which slowed reaction time because liquid oxygen could not be stored in the missile and had to be added just before launch.
In addition to missiles, the LR87 powered launch vehicles for the Gemini manned spacecraft program. Improved versions of the LR87 continued to be used in the later Titan III, Titan 34D and Titan IV launch vehicle series.