C or D call signs, as well as Group B, and any operator may choose a Group D call sign (in reality, all new licensees, except Amateur Extra, are assigned Group D call signs, since the supply of available Group C "1x3" call signs was quickly depleted with the elimination of the Element 1A Morse Code requirement for the Technician Class in 1991) The call district assignments are as follows (note that a station may not actually be located in the district indicated by the numeral in the stations's callsign) : Because the FCC will not issue long-term licenses to locations without mailing addresses, operators visiting some of these smaller islands, such as Navassa and Wake, can apply for temporary 1x1 call signs, as discussed below. Unofficial self-identification (for example, adding a /KP5 after one's call sign for Desecheo Island) is also allowed. Sequentially assigned call signs During the processing of a new license application, a call sign is selected from the available list sequentially using the sequential call sign system. This system is based on the alphabetized regional-group list for the licensee's operator class and mailing address. As of December 2015, the sequential system for Group C assigns 2-by-3 formats. Call signs begin with the letter K in Regions 1 through 10 (continental United States), and with a W (along with an area specific 2nd letter and area-specific numeral) in Regions 11 through 13 (Alaska, the Caribbean, Hawaii and insular Pacific areas). Vanity callsigns The FCC offers amateur licensees the opportunity to request a specific call sign for a primary station and for a club station. Special event 1x1 call signs The FCC allows the use of special event "1x1" call signs to denote special occasions such as a club's anniversary, a historic event or even a DXpedition. As an example, the call sign "N8S" was used for the April 2007 DXpedition to Swains Island in American Samoa. These call signs start with the letters K, N or W, followed by a single numeral from 0 to 9 then followed by a single letter from A through W, Y or Z. The letter X is not allowed as it is reserved for experimental stations. Thus, there are 750 such call signs available. Each call sign may be used for 15 days from its issue. Each station using the special 1x1 call must transmit its assigned call at least once