Apparently it is still not clear what the purpose of Nixon's secret nuclear alert of October 1969 was--to convince the Soviets that the US was determined to end the Vietnam war by whatever means necessary or to deter a Soviet nuclear strike against China.
https://fas.org/blogs/secrecy/2011/10/1969_nuclear_alert/ Whatever the purpose, it may have been riskier than Nixon and Kissinger realized:
..."At the most basic level, given that Nixon had already decided not to bomb North Vietnam and Rogers had just announced the start of SALT, these final SAC alert operations were loosely coupled to U.S. diplomatic activities at the end of October. More important, when one looks closely at the details of SAC operations, a number of the specific alert actions can be seen to have created hidden risks, dangers that ran counter to Nixon and Kissinger´s intentions. First, the president and national security adviser had ordered that no reconnaisance flights take place on the periphery of the Soviet Union so as to avoid a diplomatic incident. Yet SAC flew B-52 bombers over the Arctic ice, on routes toward the Soviet Union and back, without the use of ground-based navigational aids from radar sites in Alaska.88 Similar flights had produced an incdent earlier in the decade when a B-52 accidentally strayed into the Soviet Union´s air defense warning net, a fact not known to Washington officials in 1969 who had approved the new operation.89 Second, although Nixon and Kissinger wanted to avoid any nuclear weapons accident that would create public awareness and alarm, SAC´s improvised maintenance generation alert led to the suspension of some of the strict peacetime nuclear safety requirements. At Grand Forks AFB in North Dakota,for example, SAC issued a "temporary explosive safety waiver,” so that noncertified personnel could participate in the alert operation.90 Similarly, SAC had to issue a “quantity distance waiver” at another bomber base, permitting nuclear weapons there to be placed in closer proximity to one another than normal peacetime safety rules permit.91 Finally, and most significant, officers in the 92d Strategic Air Wing discovered that the routes and timing of the nuclear-armed bombers were poorly planned in the SEAGA alert. “Several B-52s were required to orbit in close proximity with other aircraft, an air traffic situation that was considered unsafe,” the after-action report noted.92
"Although Nixon and Kissinger wanted this to be a “safe” signal of U.S. readiness to use nuclear weapons, some increased risk of accidents and incidents was unavoidable. SAC recognized these dangers..."
http://iis-db.stanford.edu/pubs/20277/sagan_is_spr03.pdf