Murphy reaches the shore and finds a missionary settlement on the Orinoco in Venezuela, where he is treated by the pacifist Quaker Dr. Hayden.

When Murphy discovers that the U-boat is hiding farther up river under the cover of the jungle, he obsessively plots to sink it by any means, including by using a surviving Grumman J2F Duck floatplane from the Mount Kyle.

The floatplane's wounded pilot was shot dead in his hospital bed by the U-boat captain, compounding the earlier war crime of shooting the survivors in the water, in order to preserve the secret of the submarine's location.

Word comes that Germany has surrendered, but Murphy is obsessed with revenge and plans to ram the U-boat with a floating crane owned by Louis, a friendly Frenchman.

Murphy uses the crane to recover an unexploded torpedo fired earlier by the U-boat and drops it on the trapped crew, killing them.

[3] Eventually Robert Evans, head of Paramount, offered the project to the team of Peter Yates and Michael Deeley, who had made Robbery for the studio.

[11] For the scenes filmed in Malta that depict the burning of the merchant ship, O'Toole swam through water afire with oil and with explosives detonating all around him.

[12] Several of the sequences were photographed by cinematographer Douglas Slocombe, including the scenes with Murphy piloting the floatplane and the visuals along the Orinoco River.

For the extensive flying scene with many shots of the floatplane stalling and veering sharply to avoid obstacles, a camera was strapped to the wing of the aircraft.

Several Peace Corps volunteers serving in towns near the Orinoco River were recruited to play Nazi submariners.

"[12] Roger Greenspun's review in The New York Times centered on the awkwardness of the plot: "The sense of a film in which nothing quite works with anything else pervades 'Murphy's War,' and it extends from such crucial technical details as the sloppy and finally tedious cross-cutting… to the playing together of the principal actors.

"[16] A review in Variety stated: "By no means a film classic, 'Murphy's War' stands out as the kind of good, solid entertainment needed these days to fill houses.

"[17] Gene Siskel of the Chicago Tribune awarded the film two stars out of four and called it "an adventure story high in production values but low in suspense.

"[18] Charles Champlin of the Los Angeles Times wrote: "The story proceeds from the detestable to the improbable by way of the uninteresting.