1966-03-16 USA Gemini 8

Gemini 8 Swanson cover cancelled on launch day at Cape Canaveral, signed by Neil Armstrong. Dave Scott's autograph is autopen. 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 official NASA cachet on cover with a Kennedy Space Center machine cancel.
Gemini 8 NASA cachet proof (in maroon) on cover postmarked at Cape Canaveral on launch day, March 16, 1966.
Beck printed cachet cover B640 was meant for USS Goodrich, but this one went to USS Boxer.
A pair of Gemini 8 USS Boxer recovery ship covers with Beck rubber stamped cachet. Signed by Neil Armstrong and Dave Scott.
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.
Gemini 8 USS Boxer recovery ship cover applied with a red cachet that resembles the design of GTA-8 Beck's cachet - the source of this cachet is unknown. The rare USS Boxer hand cancel is usually found on such cover.
Gemini 8 USS Leonard F. Mason recovery ship's cover postmarked on return to port, Mar 25, 1966.