On July 4, 1961, while "K-19" was operating near southern Greenland, water pressure in the starboard nuclear reactor plummeted due to a coolant leak in an area of the reactor very difficult to access. The loss of coolant caused the reactor to begin to overheat, endangering the integrity of the control rods. Zateyev mistakenly believed this could lead to a nuclear explosion. The captain believed that such an explosion would damage a nearby NATO base and could cause a nuclear war between the Soviet Union and the United States. Mikhail Gorbachev later wrote that "An explosion on board the "K-19" could have been taken for a military provocation or even an attempt to launch a nuclear strike on the North American coast. An immediate response by the United States and NATO could have triggered off a Third World War." Eight crewmen died in the days that followed July 4, after working in the reactor core. However, a jury-rigged coolant system successfully averted any catastrophe. The "K-19" was later towed back to harbor and its reactors were replaced over a period of two years.