ship frequency was changed from 1,000 kHz to 500 kHz, to match the coastal station standard. Communication was generally conducted in Morse code, initially using spark-gap transmitters. Most two-way radio contacts were to be initiated on this frequency, although once established, the participating stations could shift to another frequency to avoid the congestion on 500 kHz. To facilitate communication between operators speaking different languages, standardized abbreviations were used, including a set of "Q codes" specified by the 1912 Service Regulations. Article XXI of the Service Regulations required that whenever an distress call was heard, all transmissions unrelated to the emergency had to immediately cease until the emergency was declared over. There was a potential problem if a ship transmitted a distress call: The use of 500 kHz as a common frequency often led to heavy congestion, especially around major ports and shipping lanes, and it was possible the distress message would be drowned out by the bedlam of ongoing commercial traffic. To help address this problem, the Service Regulation's Article XXXII specified that "Coastal stations engaged in the transmission of long radiograms shall suspend the transmission at the end of each period of 15 minutes, and remain silent for a period of three minutes before resuming the transmission. Coastal and shipboard stations working under the conditions specified in Article XXXV, par. 2, shall suspend work at the end of each period of 15 minutes and listen in with a wave length of 600 meters during a period of 3 minutes before resuming the transmission." During distress working all non-distress traffic was banned from 500 kHz and adjacent coast stations then monitored 512 kHz as an additional calling frequency for ordinary traffic. Later policies The silent and monitoring periods were soon expanded and standardized. For example, Regulation 44, from the 27 July 1914, edition of Radio Communication Laws of the United States, stated: "The international standard wave length is 600 meters, and the operators of all coast stations are required, during the hours the station is in operation, to 'listen in' at intervals of not more than 15 minutes and for a period not less than 2 minutes, with the receiving apparatus tuned to receive this wave length, for the purpose of determining if any distress signals or messages are being sent and to determine if the transmitting operations of the 'listening station' are causing interference with other radio communication." International