He immediately dropped down the interior ladder. The emergency dive alarm rang out an instant later, sending the crew scurrying to their stations. In the engine room, a massive clutch was engaged, killing the diesel engines and transferring drive power to a bank of battery-powered electric motors. Seawater began to slosh across the forward deck as Catalano sealed the conning tower hatch, then descended to the control room.

Normally, a well-trained crew could crash-dive a submarine in under a minute. But since it was loaded to the gills in transport mode, there was little the Italian sub could do quickly. With agonizing leisure, it finally sagged under the surface nearly two minutes after Conti had detected the approaching aircraft.

His boots clanking on the steel ladder as he descended into the control room, Catalano turned and scurried forward to his emergency dive station. The clatter of the diesel engines had fallen quiet as the sub converted to battery propulsion, and the crew mirrored the silence by speaking in hushed tones. The Barbarigo’s skipper, a round-faced man named De Julio, stood rubbing sleep from his eyes as he asked Conti if they’d been seen.

“I can’t say. I didn’t actually see the aircraft. But the moon is bright and the seas are relatively calm. I am sure we are visible.”

“We will know soon enough.”

The captain stepped to the helm station, scanning the depth gauge. “Take us to twenty meters, then full right rudder.”

The submarine’s chief steersman nodded as he repeated the command, eyeing the gauges before him as his grip tightened on a large metal steering wheel. The control room fell silent as the men awaited their fate.

A THOUSAND FEET ABOVE THEM, a lumbering British PBY Catalina flying boat released two depth charges that whirled toward the sea like a pair of spinning tops. The aircraft was not yet equipped with radar; it was the RAF plane’s rear gunner who had spotted the milky wake of the Barbarigo, angling across the rippled surface. Thrilled with his find, he pressed his nose against the acrylic window, wide-eyed, as the twin explosives splashed into the sea. Seconds later, two small geysers of spray shot into the air.

“A bit late, I believe,” the copilot said.

“I suspected as much.” The pilot, a tall Londoner who wore a clipped mustache, banked the Catalina in a tight turn with all the emotion of pouring a cup of tea.

Dropping the charges was something of a guessing game, as the submarine had already disappeared from view, though its surface wake was still visible, and the plane had to strike quickly. The airborne depth charges activated at a preset depth of only twenty-five feet. Given enough time, the sub would easily dive beyond their range.