USA 1966 Gemini 8

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.
1966 GT-8 Orbit Covers cachet cover cancelled on launch day, March 16, 1966, at Cape Canaveral, signed by Neil Armstrong and Dave Scott. Due to a critical in-space system failure of the spacecraft that threatened the lives of the astronauts, the mission was terminated much earlier than expected. The crew returned to Earth safely, recovered by USS Leonard F. Mason instead of the designated prime recovery ship, USS Boxer.
Gemini 8 Swanson cover cancelled on launch day, March 16, 1966, at Cape Canaveral. Signed by Neil Armstrong, Dave Scott's signature is autopen.
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.
The Gemini capsule landed 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.

USS Boxer cover with an early signature of Neil Armstrong on the front and rubber stamp cachet on the back.

USS Leonard Mason Beck's cover with printed cachet, signed by David Scott.

A pair of USS Boxer navy recovery ship covers, early signature of Neil Armstrong & David Scott.

Photo: Gemini 8 recovery after splashdown.

Photo: Neil Armstrong and David Scott pose with 3 Pararescue "frogmen", aboard the USS Mason.