Whaam! Prepare to be hit by Roy Lichtenstein's finest comic book hour

Roy Lichtenstein's Whaam! is an eerie modern version of the battle paintings that once decorated European palaces and council chambers. It is on a grand scale, split across two panels that together measure more than four metres in width. An American fighter unleashes a spurt of fire that blows up an enemy plane, giving the pilot no chance of escape. It is a picture of violence, but the violence is experienced third hand. The painting is meticulously translated from a DC War comic, the dots and bold colours of the original recreated by hand on an inflated scale. Our response to it is ambivalent. Is this a celebration of boys' comics, a comment on their glorification of war, a metaphor for the chilled and mechanised nature of modern killing – or nothing so serious?

It is, whatever it is, one of the most powerful monuments of 1960s pop art. Painted in 1963, Whaam! has been in the Tate collection since 1966 and has long been one of the most famous modern masterpieces in Britain. It is probably Lichtenstein's finest hour. We will have a chance to see it in the context of this artist's lifetime achievement when a retrospective of his work from the Art Institute of Chicago arrives at London's Tate Modern in 2013.

Lichtenstein made realistic paintings of an unreal world. His art is gloriously paradoxical – and the cleverest paradox is that, as in Whaam!, the unreal world turns out to have echoes in the actual one. Very early on, he hit on his comic book subject matter, and this gave his art a look it never lost – an enlarged, precise graphic style that incongruously translates efficient designs created for the page on to the generous scale of American abstract art. Like all the pop generation in America, he was working in the shadow of the abstract expressionists who in the 1940s and 50s widened the reach of painting, destroying the difference between the easel picture and the mural. Lichtenstein plays wittily on that epic scale, by filling it with comic book images that are the very opposite of the contemplative numinous clouds of Mark Rothko's visions.

In Whaam! this becomes a joke about freedom. The abstract expressionists have sometimes been accused of serving as propagandists for American culture in the cold war. The truth is more interesting. Jackson Pollock, the artist who defined abstract expressionism in the public eye, was indeed enacting freedom in the way he painted – the freedom of jazz music. With jazz 78s playing, he moved around a canvas laid on the ground, flicking and dripping paint. It was an improvisation, like Charlie Parker playing sax. In Whaam!, this free art is mockingly parodied. Lichtenstein carefully, accurately recreates an image – and that image shows a man finding freedom in machines. As he fires, the pilot obtains a sense of release. Like Jack the Dripper, he expresses himself – but does it by pressing a button.

Whaam! is still, as it was then, a comic image of American male freedom.