1856 (Jun. 16) Schleswig to New York, N.Y., folded letter endorsed per "Hammonia" and showing "Schiffes Brief Post, Hamburg, 30 Jun 1856" rimless cds, carried by Hapag Line Hammonia from Hamburg Jul. 2 to New York arriving Jul. 18, New York "6" due h.s. for the ship letter fee, Very Fine, Carried on the Maiden Voyage of Hapag Line Hammonia. One of only four recorded covers carried under the U.S.-Hamburg informal agreement prior to the 1857 Treaty. Estimate  $500 - 750. Letter carried privately from Schleswig to Hamburg, where the SchiffsBrief Post placed letter on board HAPAG Hammonia on its maiden voyage. Soon after this voyage, an informal agreement between the U.S. and Hamburg resulted in mails being carried between Hamburg and the U.S. on the HAPAG steamers. Only 10,606 letters were carried before the treaty went into effect on 1 July 1857. $0 (Image)