Canadian Commando Major Jamie Wilson (Lloyd Bridges), plans an audacious Combined Operations raid on the Axis held French port of Le Clare; if destroyed, the Germans would be stripped of the only dry dock capable of servicing their large battleships. Wilson's plan, code named Operation Mad Dog, is to ram a destroyer packed with tons of explosives into the outer gate of the dock, while his commandos cause havoc to the dock facilities and garrison, and then detonate the explosive laden destroyer. Opposed to Wilson is Royal Navy Captain Owen Franklin (Andrew Keir), whose own son was killed on Wilson's disastrous last Dieppe-type raid on the French coast at Le Plagé.
Under pressure from Winston Churchill, Wilson's plan is given the go-ahead, even though the naval craft requested for the mission are reduced to a minesweeper replacing the destroyer, no escort craft and only four motor launches. The mission's naval commander Lieutenant Commander, Don Kimberly, (Mark Eden) is blinded in a training accident while trying to save an injured commando, who dies from his injuries. With no other option, Franklin is ordered to replace Kimberly, and thus put him in direct conflict with Wilson on the journey to France. As they cross the English Channel Wilson finds himself at odds with Franklin when the supporting air raid seems to be cancelled, but, to Wilson's surprise, Franklin ignores the order to return and changes his view of both Wilson and the mission.
With a united group heading into the port, the Germans discover the approaching minesweeper and its commando carrying escort of motor launches. After briefly stalling the Germans, by pretending they are German ships, the convoy is bombarded by the coastal batteries which line the port entrance, but fail to stop the minesweeper from ramming the dock gate. As the commandos storm ashore, leaving Wilson on the minesweeper's bridge, it is hit once again, this time though, Wilson is mortally wounded. In the port's facilities a running battle rages between the Germans and the commandos, leading to Franklin being captured and taken to the German HQ.
Brought in front of the garrison commander, Colonel von Horst (Walter Gotell), Franklin is mocked for what the Germans see as a fruitless mission. Meanwhile, a German party, led by von Horst's subordinate, Captain Erich Strasser, (George Mikell) boards the minesweeper and heads for the smashed bridge where Wilson, barely alive, notices that the detonating circuit is broken. As Strasser enters the bridge, Wilson, with his last ounce of strength places the two wires together, completing the circuit; the explosives detonate, destroying the dock gate. In the German HQ, Franklin merely grins at the horror on the Germans' faces as the explosion rocks the building before commandos storm the HQ and liberate him, killing von Horst and his men. Franklin and the commandos then depart in the waiting motor launches with their mission completed.Lloyd Bridges as Major James Wilson
Andrew Keir as Captain Owen Franklin
Sue Lloyd as Sue Wilson
Mark Eden as Lieutenant Commander Donald Kimberly
Maurice Denham as Rear Admiral Sir Frederick Grafton
Glyn Owen as Forrester
Howard Pays as Lieutenant Graham
Walter Gotell as Col. von Horst
John Welsh as Admiral of the Fleet Lord William Cansley
George Mikell as Capt. Erich Strasser
Ernest Clark as Air Vice Marshal Woodbridge
Encouraged by the worldwide success of 633 Squadron, producer Walter Mirisch proposed a series of British made films with a military theme having major American stars in the lead that would comply with the Eady Levy requirements and cost no more than $1 million US$. This film was the first of the series of John C. Champion's Oakmont Productions and began shooting in May 1967. The others were Submarine X-1, Hell Boats, Mosquito Squadron, The Thousand Plane Raid and The Last Escape. Each of the films was approximately 90 minutes long making them suitable for half of a double feature and had a Hollywood star leading the cast (Lloyd Bridges in this film's case).
The film was shot at MGM-British Studios Borehamwood, Gaddesden Place Hertfordshire and Millwall Dock, St Katharine Docks and the London Docklands with special effects by the Bowie Organisation.
Composer Gerard Schurmann used his score as the basis of a 1971 concert work called Attack and Celebration. As with the other Oakmount films, portions of Ron Goodwin's score for 633 Squadron are reused.