1966-03-16 USA Gemini 8

Photo: Gemini 8 crew, David Scott (left) and Neil Armstrong (right), answering questions regarding their upcoming space mission at press conference on February 26, 1966.
Gemini 8 (GT-8), launched on March 16, 1966, was piloted by Neil A. Armstrong and David R. Scott. Gemini 8 had two major objectives, of which it achieved one. The first objective was accomplished by the commander, Neil Armstrong, who piloted the Gemini spacecraft to within 0.9m of the pre-launched Agena Target Vehicle, then slowly docked - this was the world's first orbital docking. The second objective, an extended EVA to be performed by David Scott, was cancelled due to a series of near-fatal events that followed after the docking

Atlas Agena launch cover with Sarzin cachet, postmarked on March 16, 1966, at Cape Canaveral.
Photo: Neil Armstrong at final preflight briefing on March 15, 1966, problems with the Atlas-Agena target rendezvous vehicle and the Gemini spacecraft were cleared and ready for the launch on March 16, 1966. 
1966 Gemini 8 launch cover with Orbit Covers cachet, cancelled on launch day March 16, 1966, at Cape Canaveral, signed by Neil Armstrong and Dave Scott. - RRAuction
1966 Gemini 8 launch cover with Swanson cachet, cancelled on launch day March 16, 1966, at Cape Canaveral, signed by Neil Armstrong. Dave Scott's signature is autopen.
Gemini 8 official NASA cachet on cover with a Kennedy Space Center machine cancel.
Gemini 8 NASA cachet proof (in maroon) on plain cover, postmarked at Cape Canaveral on launch day, March 16, 1966.
What followed after the successful docking were some of the most hair-raising moments in the space program history. The Gemini 8 capsule, still docked to the Agena, began to roll continuously. Never having faced such situation in simulation, the crew undocked from the Agena. It was at that point the Gemini spacecraft began to roll even faster, at a rate of one revolution per second. Both astronauts were in danger of impaired vision and loss of consciousness due to the violent motion. The problem was later discovered due to a malfunction thruster on the Gemini spacecraft. The only way to stop the motion was to use the capsule's re-entry control thrusters, which meant that Armstrong and Scott had to cut short their mission and make an emergency return to Earth.

Cover with a printed cachet depicting the Gemini 8 capsule rolling motion, postmarked March 16, 1966 at White Sands Missile Range, New Mexico. 
Photo: The Gemini capsule splashed down in the Pacific Ocean on March 17, 1966, 500 miles east of Okinawa in the Pacific Ocean and a destroyer, USS Leonard Mason, was dispatched to recover the crew and the capsule.
Had the spacecraft not made an emergency landing in the Pacific, the USS Boxer carrier in the Atlantic (i.e. the original scheduled recovery area) would be the recovery vessel for Gemini 8.
Top: Gemini 8 USS Boxer recovery ship cover signed by Neil Armstrong. This cover has a Gemini spacecraft cachet on the front and a Beck rubber stamped cachet at the back. - RegencyStamps
Bottom: Gemini 8 USS Leonard F. Mason Beck cover, signed by Dave Scott during the Novaspace signing session in 2010.
Photo: Neil Armstrong and David Scott pose with 3 Pararescue "frogmen", aboard the USS Mason.
A pair of Gemini 8 USS Boxer recovery ship covers with Beck rubber stamped cachet. Signed by Neil Armstrong and Dave Scott.
Beck printed cachet cover B640 was meant for USS Goodrich, but this one went to USS Boxer.
Gemini 8 USS Boxer recovery ship cover with a blue Beck rubber stamped cachet and a rare USS Boxer hand cancel applied on the cover.
Another rare Gemini 8 USS Boxer hand cancel on cover with a red Beck cachet applied.
Photo: Neil Armstrong and Dave Scott left Honolulu on March 18, 1966.
Gemini 8 USS Leonard F. Mason recovery ship's cover postmarked on return to port, Mar 25, 1966.
Photo: David Scott (left) and Neil Armstrong (right) at press conference on March 26, 1966.