Templeton!" The speaker was Lord Hastings, commander of the British submarine D-17. Jack Templeton, a British youth and first officer of the under-sea craft, repeated the command for which he had been waiting now for some moments. "Mr. Chadwick!" Lord Hastings' voice again. "Sir!" A third figure, standing upon the bridge-now enclosed as the submarine sank from the surface-came to attention before his commander. Frank Chadwick, an American youth and second officer of the vessel, awaited instructions. "Everything shipshape?" questioned his commander sharply. "Yes, sir. Engine-room trouble all repaired, sir." "Lookout posted forward?" "Yes, sir!" "Very well. Ten fathoms, Mr. Templeton!" Lord Hastings turned from the periscope, through which he had been peering, and for a moment gazed thoughtfully at his two young officers before speaking.