The German Government on April 20 offered to free Siegfried Paul London, an alleged American, held in custody by the Germans in Warsaw, in exchange for the release of Captain Franz von Rintelen, and threatened reprisals against Americans in Germany in case the offer was refused. Secretary Lansing, on June 4, sent a reply through the Swiss Minister, flatly refusing to comply with the demand, and indicated that if reprisals were undertaken the United States would retaliate. Indictments charging conspiracy to commit treason against the United States and to commit espionage were returned on June 7 against Jeremiah A. O'Leary, John T. Ryan, Willard Robinson, Emil Kipper, Albert Paul Fricke, Lieutenant Commander Hermann Wessels, and the Baroness Maria von Kretschmann, reported to be a kinswoman of the German Empress. Dr. Hugo Schweitzer and Rudolph Binder, now dead, were also named in the indictment. O'Leary, who had fled from justice after being indicted for conspiracy in connection with the publication of The Bull, was taken into custody in Washington on June 12. General Peyton C. March announced on June 15 that over 800,000 men had been sent abroad. A supplementary note from the Netherlands Government was delivered to the State Department on May 22, contending that Secretary Lansing's reply to the original protest against the seizure by the United States Government of Dutch merchant shipping in American ports did not fully answer the objections. German submarines began to raid shipping off the eastern coast of the United States on May 25. On June 3 it became known that twelve ships had been sunk. They were the schooners Hattie W. Dunn, the Edward H. Cole, the Edward Baird, the Isabel B. Wiley, the Samuel C. Mengel, the Samuel W. Hathaway, and the auxiliary schooner Hauppauge, and the steamships Texel, Winneconne, and the Carolina. Twelve lives were lost on the Carolina. The schooner Edward was attacked, but was saved and towed to port. Mines were set afloat by the submarines, and the tanker Herbert L. Pratt struck a mine off the Delaware Capes, but was raised and saved. Precautions were taken at once to guard against air raids on New York City and other places near the coast. On June 4 the Norwegian steamship Eibsvord was sunk off the Virginia Capes, and an American destroyer interrupted an attack on the French steamer Radioleine about sixty-five miles off the Atlantic Coast. The British steamer Harpathian was sunk off the Virginia Capes without warning on June 6, and the next day the Norwegian steamer Vinland was sunk in the same area. On June 9 the American steamer Pinar del Rio was sunk seventy-five miles off the coast of Maryland.