Project Orion was a study of a spacecraft intended to be directly propelled by a series of explosions of atomic bombs behind the craft (Nuclear pulse propulsion)

Internal explosions for nuclear pulse propulsion would not work, the blast would destroy the vehicle. For explosive nuclear pulse propulsion to work, the explosions must be external with the blast pushing against a spherical section "pusher plate" coated with a thin oil film to prevent erosion. Look up the "Orion Project" from late 50s until 63 worked on by General Atomic near San Diego.

One interesting thing about "Orion" launches is that they always take about 60 bombs to go from surface to orbit, regardless of payload weight (you just need bigger bombs).

Want to launch New York city into orbit? Orion can do it!

Plutonium can be used in nuclear reactors for nuclear propulsion of ships and submarines.

Darrell Baldwin has written:

'Space Exploration Initiative candidate nuclear propulsion test facilities' -- subject(s): Nuclear propulsion

Electricity, or propulsion in naval vessels.