This went on under the project names of Thin Slice and Heavy Chain which led to the MC-130 Combat Talons, still a key component of Air Force Special Operations Command.
With the onset of operations interdicting supplies on the Ho Chi Minh Trail in Southeast Asia during the Vietnam War, the need for aircraft specially modified for night missions became apparent, amongst other tasks.
[6] Between June and October 1967, the first aircraft, re-registered from N900V to N46598, conducted low-level night time supply drops to CIA related forces in Laos during the so-called "Secret War".
"[6] In the end, both aircraft were handed over to the 1198th OETS at Norton Air Force Base, a unit known for alleged participation in agent dropping and other clandestine missions in Southeast Asia (Project Heavy Chain).
The Squadron evaluated the two Marksman, but apparently found no use for them and scrapped both aircraft, which suffered from a chronic Invader issue of nose gear failure.