Short answers, pulled from the story.
The Halley Armada was a series of space probes sent to study Halley's Comet during its 1986 passage through the inner Solar System. Five probes succeeded, launched by the European Space Agency, the Soviet Union and France jointly through Intercosmos, and Japan's Institute of Space and Astronautical Science. NASA did not contribute a probe.
Giotto passed within 596 kilometers of Halley's nucleus on the 14th of March 1986, making it the first spacecraft to return close-up color images of a comet's core. Without targeting data from the other armada probes, the closest achievable distance would have been 4,000 kilometers.
Both Vega probes dropped a balloon probe and a lander on Venus before using Venus gravity to continue toward Halley. Vega 1 reached Halley on the 6th of March 1986 at 8,889 kilometers; Vega 2 followed on the 9th of March at 8,030 kilometers.
Japan's Institute of Space and Astronautical Science sent Sakigake primarily as a test of interplanetary mission technology; it was Japan's first probe to leave the Earth system. Data from Sakigake was then used to improve Suisei, the dedicated Halley science mission, which passed at 151,000 kilometers on the 8th of March 1986.
NASA's planned contribution, the International Comet Mission, was cancelled in November 1979. The mission would have released a European probe toward Halley while the American carrier continued to Comet 10P/Tempel. Its cancellation left the United States without a dedicated Halley probe when the comet arrived.
Challenger was carrying SPARTAN-203, a Halley observation package, when it was destroyed on the 28th of January 1986 on mission STS-51L. The disaster also led to the cancellation of STS-61-E, scheduled for the 6th of March 1986, which carried the ASTRO-1 observatory intended for astronomical observations of Halley.