Bermonsey stood forward, leaning on the table. “What’s the strength of the escorts?”
“Mid-ocean escort force group B-7,” Hardy replied. “A strong group, British, Canadian, American, some of the best corvette captains we have. They’ve been buoyed by their success in depth-charging U-boats over the last few months, and frankly, they’re spoiling for a big fight. This could be their chance to score a decisive blow, with twelve or more U-boats in that patrol line converging on the convoy and those other patrol lines also within striking range. If the escorts can sink or disable half of those U-boats, then the pendulum really begins to swing in our favor. The Germans simply can’t build enough U-boats to make up for losses like that, or replace the experienced crews.”
Bermonsey tapped the table with a pencil. “So if we did interfere with ONS-5 and send a warning, we could be preventing a convoy battle that might change the course of the war.”
“And even if we did warn them, there’s the problem with strung-out patrol lines that they may be too long for a convoy to sail around, and in so doing the convoy might be exposing itself to other U-boats in the area. As you know, it’s different with a mobile wolf-pack flotilla or a lone U-boat, where we can attempt to calculate their course from the intercepts and reroute a convoy out of danger’s way. If you try that with a patrol line, you’re just as likely to reroute the convoy into another submarine further down the line.”
Bermonsey nodded. “And as a westbound convoy, with the ships in ballast, ONS-5 is a lower-order priority than an eastbound, laden convoy. As bait for a potentially decisive U-boat battle, the ships in that convoy can therefore be considered expendable.”
He paused, looking round for any retort. Fan thought about what he had just said. A lower-order priority. She knew the fate merchant seamen most feared, being torpedoed in a heavily laden ship, knowing they could go down in seconds. But they could be just as vulnerable to torpedoing in an unladen ship, when they were less likely to have a guardian angel watching over them. And in the scenario they had just been contemplating, one that would depend on ships being hit in order for the escorts to know where to take action, the merchant seamen would be mere pawns in the battle.
“That’s the North Atlantic done, then,” Bermonsey said. “It leaves ONS-5 as our one open file, but with the tactical assessment pointing to inaction. Agreed?” There was a general murmur of consent, and he looked at the other seated naval officer. “And now for the South Atlantic.” He glanced at the wall clock. “Make it snappy, if you please.”
The other man, a lieutenant commander in the Royal Naval Volunteer Reserve who looked as if he might have been an academic in civilian life, pushed up his spectacles and peered at the lower half of the map. “It’s more straightforward, thankfully. The other actionable Ultra intercept of the past twenty-four hours concerns U-515, which is heading south off the coast of West Africa on a collision course with convoy TS-37, heading north from Takoradi in the Gold Coast to Freetown in Sierra Leone. A couple of ruled lines on compass bearings give the point of contact at about 35 degrees 15 minutes north, 45 degrees 12 minutes east, about fifty miles off the coast of Sierra Leone.”
Fan spoke for the first time. “Do we know whether U-515 has intelligence on TS-37?”
The officer looked up. “It seems so judging by the intercept course, though we don’t know how. TS-37 is one of the convoys we’ve chosen not to contact using the compromised Naval Cypher No. 3, but we suspect the existence of a Nazi spy operation in Durban who may be able to pass on information about convoy departures. Four of the ships in the convoy are carrying large consignments of manganese ore, currently in very short supply for steel and aluminum production and desperately needed to keep production of bomber aircraft up to counter the losses we’ve been enduring. The current directive from the Ministry of War Transport is that those cargos are to be considered of higher value even than munitions. Manganese is so valuable that you’ll see it disguised as pig iron in the cargo manifests of some of those ships in order not to attract the attention of spies whose information might feed back to U-boat headquarters. Corabella is carrying eight thousand and sixty tons of manganese ore; Bandar Shahpour three thousand tons. Clan Macpherson has over eight thousand tons of it, all described as pig iron. In the past, TS convoys have only rarely been hit, with Admiral Dönitz’s attention mainly having been in the North Atlantic, but with the U-boat losses there already high this year, and with more effective Allied air and sea cover, he may now look to the South Atlantic for easier pickings. My assessment is that we should do what we can to save this convoy.”
“What do we know about U-515?” Fan said.
The officer pushed up his glasses again and peered at his notes. “Kapitänleutnant Werner Henke. An exceptionally capable solo commander who sank nine ships during his first patrol last year. He has already sunk two ships in his present patrol, the British California Star off the Azores and the French Bamako off northern Senegal. If you were to choose a commander to seek out and hit a convoy on his own, he’d be your man.”
“What are our assets in the area?”
“TS-37 has a weak escort, only one corvette and three armed trawlers. That’s pretty standard for West Africa convoys at present, with the best ships and captains needed in the North Atlantic. There are two long-range Hudsons of RAF Coastal Command based at Freetown, and the convoy commodore could also call on the US escort carrier USS Guadalcanal with its Wildcats and Avengers. But Guadalcanal is currently in the mid-Atlantic, too far off to provide any kind of air cover, and barely within range for a reactive strike. By the time the aircraft arrived, the U-boat would be long gone. And none of those aircraft are specialized sub hunters.”
Bermonsey glanced at the clock again, and then at Fan. She noticed how pale and tired he looked. “Turley? Your assessment?”
“Sir.” Fan took the two convoy files from the officers opposite, one for ONS-5 in the North Atlantic and one for TS-37 off Sierra Leone, and marshalled her thoughts. She opened the files and put the diagrams showing the two convoy orders of sailing in front of her, rows and columns of ships, more than sixty of them in all. That meant perhaps eight thousand crew altogether, many of them with wives and children waking up this morning wondering where they were, with no idea of the machinations being played out that might see them through this day or condemn them to a terrible death. She quickly rehearsed in her mind what she intended to say, and then cleared her throat.
“One possibility is inaction on both convoys,” she said. “We know that assault convoys are currently in preparation in the Clyde for imminent seaborne landings in the Mediterranean, at a destination that’s still top secret. Any Ultra intercepts related to U-boats potentially targeting those convoys will absolutely have to be acted upon, all of them. Given that, it would be disastrous if by acting on an Ultra intercept now we finally take that one step too far, pushing someone in B-Dienst to realize that we’ve cracked the Enigma code and to change it just before the assault convoys sail. The destruction of one of those convoys could set back the war incalculably.”