Before he reached England, U-boat warfare was practically ended. Within ten days the submarines were recalled to their home bases. As they were returning to Germany they sank a few ships. But these were the last few examples of German frightfulness on the seas. What had brought about that tremendous change? It was not due to any lack of determination on the part of the German Admiralty, or the Kaiser. But they found that the big stick with which they were to strike was only a broken reed. The morale of their navy was shattered. Officers were willing enough to obey orders, but their men refused to fight. The U-boat crews, for years the pick and pride of the service, refused to go to sea. Germany was building hundreds of submarines, they were being turned out by the score. She might soon have sent out a dozen for every one she had when ruthless warfare began. But willing crews were lacking to man them. This was a complete reversal of previous experience. A year before U-boat duty had been the most sought-for branch of the service. Essaying long voyages in the Atlantic or the Mediterranean, cruising for weeks around the waters of England and France, their officers and men had braved many dangers, and returning were hailed by their countrymen as conquering heroes. Sinkings had been made more difficult by the convoy system. Listening devices had made it more dangerous for submarines to remain in the vicinity of naval vessels. Patrol, by surface ships and aircraft, had become more efficient. Shipping was more difficult to get at and destroy. More submarines were being sunk than in the early days. But, with all these operating against them, the U-boats, even if they could not make such high scores in tonnage, had more than an even chance to reach their home bases unscathed. Now was another danger to face, however; one that was hidden and deadly, and it had to be faced by every boat departing or returning. Some U-boats, putting out to sea from their nesting places on the German coasts, vanished utterly. No trace was left, no record of what fate befell them. Others, badly damaged, limped back to port. Survivors told of colliding with mines hidden far below the surface, whose presence could not be guessed. No vigilance could locate or action avoid them. They might run into them anywhere within hundreds of miles. This was a terror the undersea boatmen were unwilling to face. The revolt of the U-boat crews spread to other branches of the naval service, and the entire German navy began to disintegrate. The mutiny in the German sea forces, the demoralization of its personnel, has no parallel in naval history. This was undoubtedly due to various causes, but, in my belief, there was no one thing that had more influence in breaking the German morale, particularly in the U-boat service, than did the Northern Mine Barrage.