is estimated to have dropped by as much as 88%. Other countries followed suit and by 1913 the International Convention for the Safety of Life at Sea was convened and produced a treaty requiring shipboard radio stations to be manned 24 hours a day. The Radio Act of 1912 also marked the beginning of U.S. federal licensing of amateur radio operators and stations. The origin of the term "ham", as a synonym for an amateur radio operator, was apparently a taunt by professional telegraphers. World War I By 1917, World War I had put a stop to amateur radio. In the United States, Congress ordered all amateur radio operators to cease operation and even dismantle their equipment. These restrictions were lifted after World War I ended, and the amateur radio service restarted on October 1, 1919. Between the wars In 1921, a challenge was issued by American hams to their counterparts in the United Kingdom to receive radio contacts from across the Atlantic. Soon, many American stations were beginning to be heard in the UK, shortly followed by a UK amateur being heard in the US in December 1922. November 27, 1923 marked the first transatlantic two-way contact between American amateur Fred Schnell and French amateur Léon Deloy. Shortly after, the first two way contact between the UK and USA was in December 1923, between London and West Hartford, Connecticut. In the following months 17 American and 13 European amateur stations were communicating. Within the next year, communications between North and South America; South America and New Zealand; North America and New Zealand; and London and New Zealand were being made. These international Amateur contacts helped prompt the first International Radiotelegraph Conference, held in Washington, DC, USA in 1927–28. At the conference, standard international amateur radio bands of 80/75, 40, 20 and 10 meters and radio callsign prefixes were established by treaty. In 1933 Robert Moore, W6DEI, begins single-sideband voice experiments on 75 meter lower sideband. By 1934, there were several ham stations on the air using single-sideband. World War II During the German occupation of Poland, the priest Fr. Maximilian Kolbe, SP3RN was arrested by the Germans. The Germans believed his amateur radio activities were somehow involved in espionage and he was transferred to Auschwitz on May 28, 1941. After some prisoners escaped in 1941, the Germans ordered that 10 prisoners be killed in retribution. Fr. Kolbe was martyred