A series of post office robberies in the Midwest was the stated reason for the creation of the 1929 Kansas and Nebraska overprinted stamps of the Fourth Bureau Issue. The Post Office Department conceived the idea to overprint stamps with the abbreviated names of the individual states, believing that stolen overprinted state stamps would be difficult to fence in or out of state. Kansas and Nebraska were selected to initiate the experiment. Since security at large city post offices was considered adequate, only small post offices would receive the stamps. A one year supply of the 1-cent through 10-cent stamps was overprinted for Kansas and Nebraska. Higher values were not included because they were not printed by rotary press and could not easily be overprinted. The overprinted stamps could only be sold at post offices within their respective states, but they were valid for postage throughout the United States and wherever U.S regular stamps could be used. Shipments of the stamps began on April 15, 1929.