In their plan, of the 600 who had worked on the tunnels only 200 would be able to escape. The prisoners were separated into two groups. The first group of 100, called "serial offenders," were guaranteed a place and included 30 who spoke German well or had a history of escapes, and an additional 70 considered to have put in the most work on the tunnels. The second group, considered to have much less chance of success, was chosen by drawing lots; called "hard-arsers", they would have to travel by night as they spoke little or no German and were only equipped with the most basic fake papers and equipment.