Development tests of the first missiles designed by OKB-586 showed that it was possible to improve their performance specifications. That is why, in the late 1950s, OKB-586 carried out upgrades on all types of first-generation missiles. The main new features included pressurized propellant tanks and a capability to stand by in a fueled state for up to seven years.
The United States were developing the Titan II, a silo-based intercontinental ballistic missile using high-boiling components and capable of carrying highly powerful payloads. The Soviet Army did not have such an effective technology, which is why all missile design bureaus got down to the design studies into powerful heavy and super heavy missiles.
OKB-586 proposed a draft design of ballistic and orbital versions of a medium-range missile for the R-36 complex.
One of the serious challenges of the 8K67 missile development and tests was to provide best leak tightness of the propellant compartment to meet the 7-year storage requirement of a fueled missile. The problem was solved by a number of ingenious design and technological solutions. The first launch of the 8K67 missile was conducted on September 28, 1963.
At the same time, development of the 8K69 missile was in progress. The orbital missile had a unique feature: since the missile flight range was unlimited, it was capable of delivering a warhead to enemy targets from two directions: from the front and from the rear. This feature forced the potential adversary to build a dual missile defense on the borders of the defended country, in two directions. Technologically, this feature was ensured by a specific flight profile, where the orbital missile flew low-angle trajectories, including that of the artificial Earth satellite.
The first launches of the missile under the flight development test program were conducted in December 1965.
In August 1968, the 8K67P missile, a version of the 8K67 ICBM, was launched. The main difference between the missiles was that the 8K67P included a multiple reentry vehicle comprised of three warheads. The design of the new missile permitted its use in the R-36 missile complex.
Designers of the second-generation missiles followed the path of development and improvement of previous designs: key performance specifications of the missiles were greatly improved.