The attack force would avoid the German defenses, focused on the main channel of the Loire, by going in across the shallows on a spring (high) tide and on the flood (coming in), going in between midnight and 0200 hours. There was only one short window when all these requirements were met – the end of March, just seven weeks away. For almost a month, the Admiralty refused to provide a destroyer for Chariot. Mountbatten retaliated by threatening to cancel the operation, and the Admiralty finally offered the aging HMS Campbeltown (formerly the USS Buchanan, DD 131, loaned to Britain under the Lend-Lease Act).

On March 3, the Joint Chiefs gave Chariot the green light. In joint command would be Lt. Col. Charles Newman, leading the commando force, and Cmdr. Robert Ryder, running the naval operation. Lt. Cmdr. Stephen Beattie would command a heavily modified Campbeltown. Campbeltown’s topweight was lightened to reduce her draft; small-caliber guns were added, steel plating was added to protect the bridge, gunners, and commandos on deck, and 4.25 tons of high explosives were hidden in her bows to prevent a German discovery. To delay the Germans reacting during the approach up the river, two of Campbeltown’s four stacks were removed and the other two cut back and sloped, so she resembled a German Type 23 Mowe-class destroyer.

A key element of Chariot was a raid by 350 RAF bombers as a diversion. But just days before the raid, the bomber force was cut back to just 62, and to minimize French civilian casualties, most of their targets would be away from the St. Nazaire docks. Both Newman and Ryder feared that this would alert rather than divert German defenses. They were right.

The commando force was divided into three groups, each with its own targets; Group One would land by ML at the Old Mole, Group Two by ML at the Old Entrance, and Group Three would go ashore on Campbeltown. Each commando unit would comprise three parties: an assault team to eliminate immediate opposition, a demolitions team, and a heavily armed protection team. A key element of Chariot was a raid by 350 RAF bombers as a diversion. But just days before the raid, the bomber force was cut back to just 62, and to minimize French civilian casualties, most of their targets would be away from the St. Nazaire docks. Both Newman and Ryder feared that this would alert rather than divert German defenses. They were right.

At 1400 hours on March 26, 1942, the MLs slipped out of Falmouth and into the English Channel, followed an hour later by Campbeltown with two destroyers as escort. At 2000 hours the next evening, March 27, the Chariot force was 65 miles from St. Nazaire, where Ryder and Newman transferred to MGB 314 to use as their operational headquarters. The escorts slid away, and the force began its run in. Two hours later, at 2200, they saw the navigation light from the submarine HMS Sturgeon blinking the letter “M.” They were dead on course and time. The Chariot force was laid out in a two-column attack formation: The MLs of Commando Group One were on the port side and those of Group Two to starboard. Newman and Ryder’s MGB 314 was ahead and leading. Between the two columns was Campbeltown, carrying Commando Group Three, followed by ML 298 and MTB 74. Along with its modified outline, Campbeltown and the launches flew the German flag, and the signaler on Newman and Ryder’s MGB 314 carried captured German codes and signals to delay the response of the German defenses.

At 2330, Lt. Nigel Tibbits, in charge of the explosives packed into Campbeltown’s bow, activated the time pencils on the charges, while upriver the diversionary bombing raid lit the sky. The flotilla passed the Le Croisic radar station, and by 0045, they had slid undetected under the 75 mm gun battery on the Pointe de Gildas. Twice Campbeltown touched bottom on the shallows but kept going. For precious minutes, their luck held: Then a German patrol boat as well as lookouts at St. Marco spotted the flotilla but, initially at least, their report was ignored. As Newman and Ryder feared, however, the bombing raid raised German suspicions as soon as it began. Between midnight and 0100, the St. Nazaire German defense headquarters issued three warnings of a possible parachute landing or sea assault.