The day I visited the prison-turned-museum, a woman was outside it selling T-shirts, one printed with "Good Morning Vietnam" in red letters.

CNN: 'Hanoi Hilton' now holds only painful memories

The song became better known in America after its ironic use to soundtrack the carnage of war in the 1987 film Good Morning Vietnam.

BBC: Smashed Hits: How political is What A Wonderful World?